Waste treatment method

ABSTRACT

An improved oxidation process may be used to oxidize a wide variety of feedstocks. Oxidation takes place in a reactor where the feedstock is mixed with an oxidizing acid, such as nitric acid. The reaction mixture may also include another oxidizing acid such as sulfuric acid.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 15/044,354,titled “Waste Treatment Process,” filed on 16 Feb. 2016, issued as U.S.Pat. No. 9,611,158, which is a divisional of U.S. patent applicationSer. No. 13/936,932, titled “Waste Treatment Process,” filed on 8 Jul.2013, issued as U.S. Pat. No. 9,272,936, which is a continuation-in-partof U.S. patent application Ser. No. 12/416,431, titled “Aqueous PhaseOxidation Process,” filed on 1 Apr. 2009, issued as U.S. Pat. No.8,481,800, and a continuation-in-part of U.S. patent application Ser.No. 13/250,308, titled “Waste Treatment Process,” filed on 30 Sep. 2011,published as U.S. Pat. App. Pub. No. 2012/0080383, which claims thebenefit of U.S. Prov. patent application Ser. No. 61/388,164, titled“Method for Treating Sewage Sludge,” filed on 30 Sep. 2010, the entirecontents of all these documents being incorporated by reference herein.In the event of a conflict, the subject matter explicitly recited orshown herein controls over any subject matter incorporated by reference.The incorporated subject matter should not be used to limit or narrowthe scope of the explicitly recited or depicted subject matter.

INCORPORATION OF RELATED PATENT APPLICATIONS

The entire contents of the following document are incorporated byreference herein: U.S. Pat. No. 5,814,292, titled “Comprehensive EnergyProducing Methods for Aqueous Phase Oxidation,” issued on 29 Sep. 1998.In the event of a conflict, the subject matter explicitly recited orshown herein controls over any subject matter incorporated by reference.The incorporated subject matter should not be used to limit or narrowthe scope of the explicitly recited or depicted subject matter.

BACKGROUND

Modern civilization produces a large quantity of organic waste. Itoriginates from household, commercial, institutional, and industrialwaste and can include materials such as sewage sludge, animal manure,potato skins, slaughterhouse runoff, and so forth.

One of the biggest sources of organic waste is sewage material. Sewagematerial refers broadly to sewage sludge, dewatered sewage, animalwaste, lagoon sludge, and the like. Sewage material is most commonlyproduced by wastewater treatment processes such as those used inmunicipal sewage treatment plants, large scale animal productionfacilities, and the like.

Sewage material contains valuable nutrients that would be desirable tocapture and use in a safe and renewable manner such as in fertilizer.Transforming sewage material from waste into a valuable resourceproduces tremendous environmental benefits. The alternative is todispose of the sewage material in less desirable ways such asincineration or deposition in a landfill, lagoon, or the ocean.

Unfortunately, there are a number of obstacles that have prevented thewidespread use of sewage material for fertilizer. One of the biggestobstacles is the presence of toxic materials in the fertilizer such asheavy metals, pathogens, drug residues, and the like. These materialsoriginate with the sewage material and are difficult to remove when itis processed to make fertilizer. Other obstacles include the potentialfor applying too much or too little of each nutrient and the possibledetrimental effects on water quality from leaching, erosion, or runofflosses.

Regulatory restrictions have been placed on the use of fertilizerderived from sewage material due to these obstacles. There arerestrictions that prevent the fertilizer from being used on land thatexceeds a certain slope or has certain soil conditions. There arerestrictions on how close it can be applied to homes, wells, streams,roads, and property lines. There are also restrictions that limit thequantity of heavy metals (arsenic, cadmium, chromium, cobalt, copper,mercury, molybdenum, nickel, lead, selenium, and zinc) that can beapplied to a given area. Once these limits are reached, no morefertilizer can be added, but the land can still be used for normal cropproduction.

Numerous attempts have been made over the years to develop a process todispose of organic waste materials in an effective and cost efficientmanner. Unfortunately, most of these processes consume large amounts ofenergy, emit noxious gases, and rarely achieve the desired conversionrate.

An earlier process oxidized the waste material in a solution of nitricand sulfuric acid. The reaction occurred in a pressurized reactor thatwas maintained at a temperature of no more than 210° C. Oxygen gas wasadded to facilitate the reaction and breakdown of the waste material.

The process successfully transformed the waste material into materialssuch as oxygen, nitrogen, water, carbon dioxide, and so forth. However,the solution included a high concentration of nitric and sulfuric acidand much of it was consumed in the process. This made the economics ofthe process challenging since it consumed large amounts of relativelyexpensive acid and produced mostly low value end products.

A number of embodiments of an improved process for eliminating wastematerial and/or transforming it into a commercially valuable end productare described below. The process is especially suited for convertingsewage materials into fertilizer and other useful materials. The processreduces or eliminates many of the problems and disadvantages associatedwith conventional processes.

SUMMARY

A number of representative embodiments are provided to illustrate thevarious features, characteristics, and advantages of the waste treatmentprocess. The embodiments are provided primarily in the context oftreating sewage material. It should be understood, however, that many ofthe concepts can be used in a variety of other settings, situations, andconfigurations. For example, the features, characteristics, advantages,etc., of one embodiment can be used alone or in various combinations andsub-combinations with one another.

A waste treatment process includes reacting a feedstock in a reactorwith a first oxidizing acid and nitric acid. The process can be used totreat any feedstock. Examples of suitable feedstocks include sewagematerial such as dewatered sewage, municipal sludge cake, animal manure,and the like. Other feedstocks include potato skins, produce waste,municipal waste, farm waste, and the like. In one embodiment, theprocess is used to treat sewage material and transform it intofertilizer and/or biofuel.

In one embodiment, the feedstock is an organic feedstock. The organicfeedstock can include other materials. However, it is preferable for thefeedstock to include, on a dry basis, a substantial amount of organicmaterial thereby rendering it an organic feedstock. In one embodiment,the organic feedstock includes 20 wt % to 100 wt % organic material on adry basis (i.e., excluding water).

The feedstock is oxidized in an aqueous reaction mixture that includesone or more oxidizing acids. The oxidizing acid is supplied in an amountthat is sufficient to oxidize the feedstock and produce the desiredreaction products. In one embodiment, the feedstock and the oxidizingacid are part of a reaction mixture that includes no more thanapproximately 7.5 wt % oxidizing acid. The reaction mixture can alsohave a pH of approximately 0.5 to 2.0. The reaction mixture can includeoxidizing acids such as sulfuric acid and/or nitric acid.

The amount of solids in the feedstock and oxidizing acid in the reactionmixture can vary widely depending on the circumstances. In general,these materials should be supplied in amounts sufficient for thereaction to proceed relatively quickly (10 s to 2 min reaction time) andstill produce desirable reaction products—e.g., a nonviscous liquid thatincludes a readily separable solid fraction.

The weight ratio of solids to oxidizing acid in the reaction mixture canbe at least 0.2. The weight ratio of solids to the first oxidizing acidcan be at least 0.3. The weight ratio of solids to nitric acid can be atleast 0.5. If the feedstock is an organic feedstock, then the weightratio of organic material to oxidizing acid in the reaction mixture canbe at least 0.2. The weight ratio of organic material to the firstoxidizing acid can be at least 0.3. The weight ratio of organic materialto nitric acid can be at least 0.5.

The feedstock can be processed before being fed to the reactor to giveit uniform physical properties and to make it better suited to berapidly and efficiently oxidized. This can include comminuting thefeedstock to a uniform size that allows the feedstock to easily enterthe reactor, combining the feedstock with recycled effluent from thereactor, and/or combining the feedstock with one or more oxidizing acidsbefore the feedstock enters the reactor.

Oxygen gas can be supplied to the reactor to facilitate oxidation of thefeedstock and potentially reoxidize the reduction products of theoxidizing acid thereby regenerating the acid in situ. The oxygen gas canbe added to the reaction mixture in a variety of ways. For example, itcan be injected into the reaction mixture, added to the headspace of thereactor, bubbled into the liquid, or added in any other suitable manner.The reactor is maintained at suitable pressures and temperatures tofacilitate the reaction between the organic material and the oxidizingacid and/or regeneration of the oxidizing acid.

The process produces a runny effluent having a solid fraction (or solidcomponent) and a liquid fraction (or liquid component). The solidfraction is 2 to 10 wt % of the effluent and the liquid fraction is therest. The hydrocarbon material in the solid fraction can include atleast 25 wt % fatty acid esters, at least 50 wt % fatty acid esters, orat least 75 wt % fatty acid esters. The fatty acid esters can bemono-alkyl esters of long chain fatty acids. The weight ratio of carbonto nitrogen in the solid fraction is more than two times the weightratio of carbon to nitrogen in the liquid fraction.

The effluent exits the reactor and is cooled. The pressure is alsoreduced and any dissolved gas separates. The effluent can be vigorouslyagitated to speed up the separation and make it more complete. Thesolids are separated from the effluent.

The liquid fraction of the effluent can contain heavy metals, especiallyif the feedstock is sewage material. The heavy metals can be separatedin a variety of ways. One way is to allow the liquid fraction to situndisturbed for a sufficient period of time for the heavy metals toprecipitate out of the solution. The remaining liquid can be drawn offthe top and mixed with ammonia to neutralize any residual acid andproduce liquid fertilizer. Another way to remove the heavy metals iswith an ion exchange material.

The solid fraction can also include heavy metals. These can be removedusing a variety of techniques. In one embodiment, the heavy metals areremoved from the liquid fraction in the manner described above and theresulting liquid can be used as a solvent to extract additional heavymetals from the solid effluent. The heavy metals can then be separatedfrom the liquid by precipitation.

It should be appreciated that all pressures referred to herein are gaugepressures unless stated otherwise. Also, all references to molarity aregiven at standard conditions for temperature and pressure—i.e., 0° C.and 101.325 kPa—unless stated otherwise.

The foregoing and other features, utilities, and advantages of thesubject matter described herein will be apparent from the following moreparticular description of certain embodiments as illustrated in theaccompanying drawings.

The Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. The Summary and the Background are not intended to identifykey concepts or essential aspects of the disclosed subject matter, norshould they be used to constrict or limit the scope of the claims. Forexample, the scope of the claims should not be limited based on whetherthe recited subject matter includes any or all aspects noted in theSummary and/or addresses any of the issues noted in the Background.

DRAWINGS

The preferred and other embodiments are disclosed in association withthe accompanying drawings in which:

FIG. 1 is a block diagram of one embodiment of a process for oxidizingan organic feedstock that includes a feedstock processing system, areaction system, and an effluent processing system.

FIG. 2 is a block diagram of one embodiment of the feedstock processingsystem in FIG. 1.

FIG. 3 is a block diagram of another embodiment of the feedstockprocessing system in FIG. 1.

FIG. 4 is a block diagram of one embodiment of the reaction system inFIG. 1.

FIG. 5 is a block diagram of one embodiment of the effluent processingsystem in FIG. 1.

FIG. 6 is a block diagram of another embodiment of the feedstockprocessing system in FIG. 1.

FIG. 7 is a block diagram of another embodiment of the reaction systemin FIG. 1.

FIG. 8 is a block diagram of another embodiment of the effluentprocessing system in FIG. 1.

DETAILED DESCRIPTION

The process described, in its various embodiments, can be used tooxidize a wide variety of materials. The process is especially suitedfor oxidizing organic materials such as sewage materials and food waste,but it can also be used to oxidize other materials as well. Specificmaterials that may be oxidized using this process include, but are notlimited to, food waste and municipal and farm waste including dewateredsewage, municipal sludge cake and animal manure.

Referring to FIG. 1, a block diagram of an improved aqueous phaseoxidation process 100 is shown. The process 100 includes a feedstockprocessing system 104, a reaction system 106, and an effluent processingsystem 108. The process is conceptually divided into the three systems104, 106, 108 only for the purpose of describing it. It should beappreciated that the dividing line between each system 104, 106, 108 issomewhat arbitrary and does not represent a hard and fast boundary.Indeed, various components of one system could just as easily beconsidered part of a different system. With this in mind, the threesystems 104, 106, 108 should be viewed as a convenient conceptualframework from which to describe the overall operation of the process.

The raw feedstock 102 enters the feedstock processing system 104 whereit is modified and/or processed to produce a primary feedstock. Theprimary feedstock is fed to the reaction system 106 where it isoxidized. The effluent from the reaction system 106 enters the effluentprocessing system 108 where it is separated and/or otherwise processedto produce final products 110. Each system 104, 106, 108 is described ingreater detail.

The raw feedstock 102 can be any suitable material capable of beingoxidized. In one embodiment, the raw feedstock 102 is an organicfeedstock that includes organic material such as that found in sewagematerial, farm waste, municipal waste, food processing waste (e.g.,potato skins), and the like.

The organic feedstock can include any amount of organic material. Forexample, the organic feedstock can include, on a dry basis, at leastapproximately 20 wt % organic material, at least approximately 50 wt %organic material, at least approximately 75 wt % organic material, atleast approximately 80 wt % organic material, at least approximately 90wt % organic material, or at least approximately 95 wt % organicmaterial. The organic feedstock can include, on a dry basis,approximately 20 wt % to approximately 100 wt % organic material.

The raw feedstock 102 can also include any suitable amount of solids. Itis generally preferable for the raw feedstock 102 to include enoughliquid to make it possible to pump the raw feedstock 102 through thesystem. However, it should be appreciated that the rheologicalproperties of the feedstock 102 can be adjusted as desired by adding orremoving water or acids.

In one embodiment, the raw feedstock 102 includes approximately 1 to 95wt % solids, approximately 1 to 50 wt % solids, or approximately 2 to 30wt % solids. The raw feedstock 102 can include at least 1 wt % solids,at least 2 wt % solids, or at least 3 wt % solids. The raw feedstock 102can include no more than 95 wt % solids, no more than 50 wt % solids, orno more than 30 wt % solids.

Sewage material is one of the most common forms of raw feedstock 102oxidized in the process. The rest of the description refers to the rawfeedstock 102 as sewage material 102 to reflect this. It should beappreciated, however, that virtually any raw feedstock, particularlythose that contain organic material, can be the raw feedstock 102.

The sewage material 102 can be supplied in any of a number of differentforms. For example, it can be supplied as a slurry or bulk solids. Inone embodiment, the sewage material is supplied as a readily pourableliquid that includes approximately 2 to 20 wt % solids, approximately 3to 10 wt % solids, or, desirably, 4 to 6 wt % solids (e.g.,approximately 5 wt % solids). The solids are largely if not entirelyorganic materials with the exception of trace minerals and heavy metalsthat may be present.

FIG. 2 shows a block diagram of one embodiment of a feedstock processingsystem 200. The sewage material 102 initially enters a preprocessingsystem 206 where the physical characteristics of the sewage material 102are altered to make the sewage material 102 easier to oxidize.

In one embodiment, the sewage material 102 is dewatered in thepreprocessing system 206 to produce a dewatered feedstock. Dewateringrefers broadly to any process that reduces the water content of thesewage material 102. There are numerous ways that the sewage material102 can be dewatered.

In one embodiment, the sewage material 102 is dewatered by mixing aflocculant with the sewage material 102 causing the solids to clumptogether. The solids can then be separated using any suitable separationdevice or technique. In another embodiment, the sewage material 102 isdewatered without the use of a flocculant.

Additional examples of suitable techniques and devices for dewateringthe sewage material 102 include evaporation in a lagoon or sand dryingbed or mechanical separation using a rotary drum vacuum filter,centrifuge, belt filter press, plate and frame press, or vacuumdewatering bed.

In another embodiment, the sewage material 102 is ground, cut, orotherwise comminuted in the preprocessing system 206 to reduce the sizeof the solid particles, improve the uniformity of the feedstock, and/ormake the feedstock more amenable to evenly controlled pumping. Forexample, the preprocessing system 206 can include one or more grinders,cutters, choppers, and the like which grind, cut, and chop the sewagematerial 102 until it reaches the desired consistency.

In one embodiment, the sewage material 102 passes through a cutter and agrinder positioned in series. The sewage material 102 is pumped as abatch into a tank where it is circulated through a cutter until thesolids reach a uniform size. The sewage material 102 is pumped as abatch into another tank where it is circulated through a grinder thatfurther reduces the particle size of the solids. The sewage material 102is then pumped into another tank where it is stored for furtherprocessing.

It is often desirable to control the size and uniformity of the sewagematerial 102 for a number of reasons. A uniform feedstock is easier tofeed into the reactor 402, which is often operated at an elevatedpressure, without plugging the entry opening. Also, a uniform feedstockmakes it easier to control the reaction rate in the reactor 402.

Larger particles generally need longer residence times and/or more acidto sufficiently react. If the feedstock contains both large and smallparticles, the large particles tend to dictate the residence time. Thus,it is desirable to create a feedstock that generally has small, uniformparticles. This is especially true when the feedstock includes organicmatter such as that contained in the sewage material 102.

A feedstock with small uniform, particles reacts faster than a feedstockwith a wide distribution of particle sizes. Increasing the reaction ratecan also make it possible to reduce the size of the reactor 402 and/orincrease the feed rate of the feedstock into the reactor 402. Eitheradjustment has a beneficial effect on the economics of the process 100.

In one embodiment, the largest dimension of at least approximately 95%of the particles in the comminuted feedstock is no more thanapproximately 7 mm, no more than approximately 4 mm, no more thanapproximately 2.5 mm, desirably, no more than approximately 1.5 mm, or,suitably, no more than approximately 0.5 mm. In another embodiment, thelargest dimension of at least approximately 98% of the particles in thecomminuted feedstock is no more than approximately 7 mm, no more thanapproximately 4 mm, no more than approximately 2.5 mm, desirably, nomore than approximately 1.5 mm, or, suitably, no more than approximately0.5 mm. In yet another embodiment, the largest dimension of at leastsubstantially all of the particles in the comminuted feedstock is nomore than approximately 7 mm, no more than approximately 4 mm, no morethan approximately 2.5 mm, desirably, no more than approximately 1.5 mm,or, suitably, no more than approximately 0.5 mm.

It should be appreciated that the sewage material 102 can be comminutedat other locations in the feed processing system 200 besides thepreprocessing system 206. For example, the sewage material 102 can becomminuted in the mixing vessel 208 as part of the process of mixing thevarious materials together. The sewage material 102 can also becomminuted in a separate vessel or grinder before entering the mixingvessel 208. Numerous variations are possible.

It should be appreciated that it is not required to preprocess thesewage material 102. In some embodiments, such as the one shown in FIG.3, the sewage material 102 may not undergo preprocessing 206.

The preprocessed feedstock is mixed with recycled effluent 204, a firstoxidizing acid 210, and, optionally, a second oxidizing acid 212 in themixing vessel 208 to produce a primary feedstock. The amount of recycledeffluent 204 and/or oxidizing acids 210, 212 added to the mixing vessel208 should be sufficient to create a slurry that doesn't plug or clogthe equipment and/or facilitates later processing and transport.

The amount of recycled effluent 204 added can vary depending on thecharacteristics of the sewage material 102. Generally, larger quantitiesof the recycled effluent 204 are used if the sewage material 102 is dry,while smaller quantities, or possibly none at all, are used if thesewage material 102 already includes a suitable amount of liquid. In oneembodiment, the weight ratio of the recycled effluent 204 to the sewagematerial 102 in the mixing vessel 208 is approximately 1.5 to 4 or,desirably, approximately 2 to 3.

The recycled effluent 204 can be supplied at an elevated temperature toheat the sewage material 102 when the two are mixed together. Theeffluent from the reactor 402 (FIG. 4) is heated by the exothermicoxidation of the sewage material 102 and/or by a heater that is part ofthe reactor 402. The recycled effluent 204 can be at an elevatedtemperature simply because it has not cooled (either naturally or due toactive cooling) after leaving the reactor 402. The recycled effluent 204can also be heated in a heat exchanger to keep it at an elevatedtemperature.

In one example, described in greater detail below, the recycled effluent204 and/or the primary feedstock is heated in a heat exchanger usingheat from the effluent that has just left the reactor 402. The recycledeffluent 204 can be stored in an insulated tank or vessel before beingmixed with the sewage material 102 to maintain it at an elevatedtemperature. The resulting feedstock can be significantly above ambienttemperature. In one embodiment, the recycled effluent 204 is supplied ata temperature of approximately 40° C. to 90° C. or, desirably, 50° C. to75° C. The primary feedstock can be approximately 37° C. to 50° C.

The recycled effluent 204 and the acids 210, 212 are added to thepreprocessed feedstock before it enters the reactor 402. The amount ofrecycled effluent 204 added is just enough to lower the viscosity of thepreprocessed feedstock to allow it to be fed into the reactor 402. Ithas been found that pre-treating the preprocessed feedstock in thismanner may increase the reaction rate in the reactor 402. The primaryfeedstock is preferably fed into the reactor 402 immediately after therecycled effluent 204 and the acids 210, 212 have been added. It shouldbe appreciated that the preprocessed feedstock can also be fed into thereactor without mixing it with the recycled effluent 204 and/or theacids 210, 212.

The first oxidizing acid 210 and the second oxidizing acid 212 are addedto the mixing vessel 208 until the concentration of the acids 210, 212in the primary feedstock, excluding solids (i.e., the concentration ofthe primary feedstock excluding the solids portion), is approximatelythe same as the concentration of the acids 210, 212, respectively, inthe reactor 402 at start-up. In one embodiment, the acids 210, 212 areadded until the pH of the primary feedstock is about 1.0. The feedstockis about neutral and the pH of the recycled effluent 204 is about 1.3 soenough acids 210, 212 are added to reach a final pH for the primaryfeedstock of about 1.0

The first oxidizing acid 210 can be sulfuric acid, and the secondoxidizing acid 212 can be nitric acid. The acids function as theoxidizing agent to oxidize the sewage material 102. In general, it ispreferable to use more sulfuric acid than nitric acid. Sulfuric acid isa less aggressive oxidizing agent so it is less likely to excessivelyreact with the sewage material 102 and produce low value products. Forexample, a higher amount of sulfuric acid relative to nitric acidproduces longer chain hydrocarbons and other valuable organic products,while a higher amount of nitric acid relative to sulfuric acidaggressively oxidizes the sewage material to low value products such ascarbon dioxide, water, nitrogen gas, etc. Sulfuric acid is also lessexpensive than nitric acid.

Any suitable amount of the first oxidizing acid can be used. In oneembodiment, the first oxidizing acid is added to achieve a concentrationin the primary feedstock, excluding solids, of at least approximately0.5 wt %, desirably, at least approximately 1 wt %, or, suitably, atleast approximately 1.5 wt %. In another embodiment, the first oxidizingacid is added to achieve a concentration in the primary feedstock,excluding solids, of no more than approximately 5 wt %, desirably, nomore than approximately 3.5 wt %, or, suitably, no more thanapproximately 3 wt %. In yet another embodiment, the first oxidizingacid is added to achieve a concentration in the primary feedstock,excluding solids, of approximately 0.5 wt % to 5 wt %, desirably,approximately 1 wt % to 3.5 wt %, or, suitably, approximately 1.5 wt %to 3 wt %.

On a molar basis, in one embodiment, the first oxidizing acid is addedto achieve a concentration in the primary feedstock, excluding solids,of at least approximately 0.052 mol/L, desirably, at least approximately0.10 mol/L, or, suitably, at least approximately 0.16 mol/L. In anotherembodiment, the first oxidizing acid is added to achieve a concentrationin the primary feedstock, excluding solids, of no more thanapproximately 0.52 mol/L, desirably, no more than approximately 0.36mol/L, or, suitably, no more than approximately 0.31 mol/L. In yetanother embodiment, the first oxidizing acid is added to achieve aconcentration in the primary feedstock, excluding solids, ofapproximately 0.052 mol/L to 0.52 mol/L, desirably, approximately 0.10mol/L to 0.36 mol/L, or, suitably, approximately 0.16 mol/L to 0.31mol/L.

The weight ratio of solids in the primary feedstock to the firstoxidizing acid can be at least approximately 0.3, at least approximately0.5, at least approximately 0.7, at least approximately 1, at leastapproximately 1.5, or at least approximately 2. The weight ratio ofsolids in the primary feedstock to the first oxidizing acid can also beapproximately 0.3 to approximately 30, approximately 0.5 toapproximately 25, approximately 0.7 to approximately 20, approximately 1to approximately 15, approximately 1.5 to approximately 10, orapproximately 2 to approximately 7.5. The weight ratio of solids in theprimary feedstock to the first oxidizing acid can be no more thanapproximately 30, no more than approximately 25, no more thanapproximately 20, no more than approximately 15, no more thanapproximately 10, or no more than approximately 7.5. The weight ratio ofsolids in the primary feedstock to the first oxidizing acid can be thesame as the weight ratio of organic material in the primary feedstock(regardless whether the organic material is solid) to the firstoxidizing acid.

Any suitable amount of second oxidizing acid can be used. In oneembodiment, the second oxidizing acid is added to achieve aconcentration in the primary feedstock, excluding solids, of at leastapproximately 0.05 wt %, desirably, at least approximately 0.1 wt %, atleast approximately 0.5 wt % or at least approximately 1 wt %. Inanother embodiment, the second oxidizing acid is added to achieve aconcentration in the primary feedstock, excluding solids, of no morethan approximately 5 wt %, desirably, no more than approximately 3 wt %,no more than approximately 2 wt %, or, suitably, no more thanapproximately 1 wt %. In yet another embodiment, the second oxidizingacid may be added to achieve a concentration in the primary feedstock,excluding solids, of approximately 0.05 wt % to 5 wt %, desirably,approximately 0.1 wt % to 3 wt %, or, suitably, approximately 0.5 wt %to 2 wt %.

On a molar basis, in one embodiment, the second oxidizing acid is beadded to achieve a concentration in the primary feedstock, excludingsolids, of at least approximately 0.008 mol/L, at least approximately0.016 mol/L, at least approximately 0.08 mol/L, or at leastapproximately 0.16 mol/L. In another embodiment, the second oxidizingacid may be added to achieve a concentration in the primary feedstock,excluding solids, of no more than approximately 0.80 mol/L, desirably,no more than approximately 0.48 mol/L, no more than approximately 0.32mol/L, or, suitably, no more than approximately 0.0.16 mol/L. In yetanother embodiment, the second oxidizing acid may be added to achieve aconcentration in the primary feedstock, excluding solids, ofapproximately 0.008 mol/L to 0.80 mol/L, desirably, approximately 0.016mol/L to 0.48 mol/L, or, suitably, approximately 0.08 mol/L to 0.32mol/L.

The weight ratio of solids in the primary feedstock to the secondoxidizing acid can be at least approximately 0.5, at least approximately0.75, at least approximately 1, at least approximately 2, at leastapproximately 5, or at least approximately 7. The weight ratio of solidsin the primary feedstock to the second oxidizing acid can also beapproximately 0.5 to approximately 50, approximately 0.75 toapproximately 45, approximately 1 to approximately 40, approximately 2to approximately 35, approximately 5 to approximately 30, orapproximately 7 to approximately 25. The weight ratio of solids in theprimary feedstock to the second oxidizing acid can be no more thanapproximately 50, no more than approximately 45, no more thanapproximately 40, no more than approximately 35, no more thanapproximately 30, or no more than approximately 25. The weight ratio ofsolids in the primary feedstock to the second oxidizing acid can be thesame as the weight ratio of organic material in the primary feedstock(regardless whether the organic material is solid) to the secondoxidizing acid.

The total amount of oxidizing acid in the primary feedstock can varywidely. In one embodiment, the total amount of acid in the primaryfeedstock, excluding solids, is at least approximately 0.3 wt %,desirably, at least approximately 0.5 wt %, or, suitably, at leastapproximately 1 wt %. In another embodiment, the total amount of acid inthe primary feedstock, excluding solids, is no more than approximately7.5 wt %, desirably, no more than approximately 5 wt %, no more thanapproximately 3 wt %, or, suitably, no more than approximately 2 wt %.In yet another embodiment, the total amount of acid in the primaryfeedstock, excluding solids, is approximately 0.3 wt % to 7.5 wt %,desirably, approximately 0.5 wt % to 5 wt %, or, suitably, approximately1 wt % to 3 wt %.

Any ratio of the first oxidizing acid the second oxidizing acid can beused. In one embodiment, the ratio of first oxidizing acid to secondoxidizing acid in the primary feedstock is at least approximately 0.5,at least approximately 1, at least approximately 2, desirably, at leastapproximately 3, or, suitably, at least approximately 4. In anotherembodiment, the second oxidizing acid may be eliminated entirely oradditional acids may be added. For example, the process may be operatedusing only the first oxidizing acid.

The weight ratio of solids in the primary feedstock to the total amountof oxidizing acid can be at least approximately 0.2, at leastapproximately 0.5, at least approximately 0.75, at least approximately1, or at least approximately 1.5. The weight ratio of solids in theprimary feedstock to the total amount of oxidizing acid can also beapproximately 0.2 to approximately 20, approximately 0.5 toapproximately 15, approximately 0.75 to approximately 10, approximately1 to approximately 7.5, or approximately 1.5 to approximately 5. Theweight ratio of solids in the primary feedstock to the total amount ofoxidizing acid can be no more than approximately 20, no more thanapproximately 15, no more than approximately 10, no more thanapproximately 7.5, or no more than approximately 5. The weight ratio ofsolids in the primary feedstock to the total amount of oxidizing acidcan be the same as the weight ratio of organic material in the primaryfeedstock (regardless whether the organic material is solid) to thetotal amount of oxidizing acid.

The primary feedstock can have any suitable pH. In one embodiment, thepH of the primary feedstock is at least approximately 0.5, desirably, atleast approximately 0.7, or, suitably, at least approximately 0.85. Inanother embodiment, the pH of the primary feedstock is no more thanapproximately 1.75, desirably, no more than approximately 1.5, or,suitably, no more than approximately 1.25. In another embodiment, the pHof the primary feedstock is approximately 0.5 to 1.75, desirably,approximately 0.7 to 1.5, or, suitably, approximately 0.85 to 1.25.

The mixing vessel 208 can be any suitable tank, pipe, or other vesselthat is capable of holding and/or mixing the materials. The mixingvessel 208 should be made of a material that is chemically resistant tothe acids 210, 212. Suitable materials include plastic, titanium,stainless steel, zirconium, and the like. In one embodiment, the mixingvessel 208 is a plastic lined steel vessel (e.g., carbon steel orstainless steel lined with polytetrafluoroethylene (PTFE),polyfluoroalkoxy (PFA), or other fluoropolymers). In another embodiment,the reactor 402 can be made of G-35 stainless steel, or Zirconium 702.

As shown in FIG. 2, the primary feedstock exits the mixing vessel 208and is stored in a storage vessel or tank 214 before it is fed into thereactor 402. In one embodiment, the storage vessel 214 is insulated tomaintain the temperature of the primary feedstock and conserve energy.It should be noted that it is generally not desirable to store theprimary feedstock for a long period of time before feeding it into thereactor 402. The presence of the acids 210, 212 may cause the primaryfeedstock to separate and the texture to change in a way that can makeit difficult to feed into the reactor 402.

The primary feedstock is now prepared to be fed into the reactor 402.This can be accomplished using a variety of different techniques andequipment. In one embodiment, the primary feedstock is fed into thereactor 402 by one or more feeding devices 216.

The feeding device 216 feeds the primary feedstock into the reactor 402at a steady rate or approximately steady rate. Relatively minorfluctuations in the feed rate can cause large fluctuations in thereaction under certain situations such as the conditions present duringbatch reactions. If the feed rate drops, the reactor 402 is starved andif the feed rate climbs, the reactor 402 is overfed.

The reaction may be, in some situations, more sensitive to feed ratefluctuations than to other parameters such as temperature and pressure.For this reason, it is desirable to tightly control the feed rate.However, this is not a simple matter since the reactor 402 canexperience relatively large fluctuations in pressure and temperature.The pressure swings make it particularly difficult to feed the primaryfeedstock into the reactor 402 at a steady rate.

The feeding device 216 can have any suitable configuration that allowsit to feed the primary feedstock at a steady rate. In one embodiment,the feeding device 216 is actuated or powered hydraulically orpneumatically. For example, the feeding device 216 may include one ormore hydraulic or pneumatic rams that dispense or force the primaryfeedstock into the reactor 402. One example of a suitable hydraulicallypowered feeding device is a cycling ram pump.

The feeding device 216 can also be actuated or powered by a gearmotor.For example, the feeding device 216 includes a gearmotor that turns ascrew which, in turn, feeds the primary feedstock into the reactor 402.The feeding device 216 can be configured so that pressure fluctuationsin the reactor 402, even up to the reactor's safe operating pressurelimit of approximately 13,800 kPa, do not significantly change the feedrate.

In one embodiment, the feeding device 216 is an extruder and/or injectorthat is hydraulically, pneumatically, or gear actuated. Multiple feedingdevices 216 can be positioned in parallel to provide an uninterruptedsupply of the primary feedstock to the reactor 402. The multiple feedingdevices 216 can be sequentially activated and refilled so that when onefeeding device 216 is injecting the feedstock into the reactor 402,another feeding device 216 is refilled with the primary feedstock. Also,the use of multiple feeding devices 216 is advantageous because itallows one or more devices 216 to be offline for maintenance or repairswhile the remainder of the devices 216 provide a continuous supply offeedstock to the reactor 402.

The feeding device 216 can feed the primary feedstock into the reactorat a rate that fluctuates no more than approximately 10% per hour,desirably, no more than approximately 5% per hour, or, suitably no morethan approximately 2% per hour. In another embodiment, the feedingdevice 216 feeds the primary feedstock into the reactor at a feed ratethat is approximately constant. The feeding device 216 is capable ofmaintaining the desired feed rate even though the pressure in thereactor 402 can vary from approximately 1,035 kPa to 6,900 kPa.

The operation of the feeding device 216 is as follows. The feedingdevice 216 is initially at atmospheric pressure when it is filled withthe primary feedstock from the storage vessel 214. The feeding device216 is isolated from the high pressure in the reactor 402 by a valve220. Once the feeding device 216 is full of primary feedstock, a valve218 is closed to isolate the feeding device 216 from the low pressureenvironment of the primary feedstock storage 214. The valve 220 isopened and the feeding device 216 injects the primary feedstock into thereactor 402.

In this manner, the feeding device 216 can be selectively exposed toatmospheric pressure when it is filled with the primary feedstock andexposed to the high pressure of the reactor 402 when it is feeding theprimary feedstock into the reactor 402. The valves 218, 220 selectivelyisolate the feeding device 216 from the reactor 402 during feeding andrefilling operations. As explained above, the valve 218 is closed andthe valve 220 is open when the feeding device 216 injects the primaryfeedstock into the reactor 402, and the valve 220 is closed and thevalve 218 is open when the feeding device 216 is refilled with theprimary feedstock.

The valves 218, 220 may also be used to isolate the feeding device 216so that it can be repaired while the reactor 402 remains in operation.Moreover, the valves 218, 220 can also prevent backflow from the reactor402 into the feedstock processing system 104 during an overpressureevent. It should be appreciated that although the valves 218, 220 aredepicted as being separate from the feeding device 216, the valves 218,220 may be provided as integral components of the feeding device 216.

A pressure release system 222 may be provided that allows the feedingdevice 216 to transition from a high pressure state to a low pressurestate without causing undue wear on the components and/or blowback intothe primary feedstock storage 214 when the valve 218 is opened. In oneembodiment, the pressure release system may include a tank that iscapable of absorbing excess pressure.

In another embodiment, the feeding device 216 feeds the primaryfeedstock into the reactor 402 at a rate that is not steady, butfluctuates somewhat. For example, a single feeding device 216 can beused that is repeatedly refilled and activated. The reactor 402 onlyreceives feedstock when the feeding device 216 is activated so that nofeedstock enters the reactor 402 while the feeding device 216 isrefilled. The refill time can be relatively short compared to theactivation time to minimize the effect on the reaction.

It should be appreciated that the feedstock processing system 104 can beconfigured in a number of other ways besides that shown in FIG. 2. Forexample, FIG. 3 shows a block diagram of another embodiment of afeedstock processing system 300. This embodiment is similar to thefeedstock processing system 200 except that the sewage material 102 isnot preprocessed before entering the mixing vessel 208. Also, theprimary feedstock is not stored in a separate storage vessel.

The feedstock processing system 300 can be used in a variety ofsituations such as where the sewage material 102 is sewage sludge or abulk solid material. Also, the mixing vessel 208 can function as astorage vessel so that the primary feedstock is drawn from the mixingvessel 208 into the reactor 402. Numerous other changes to the feedstockprocessing system 104 are also contemplated.

Referring to FIG. 4, a block diagram is shown of one embodiment of areaction system 400. The reaction system 400 includes the reactor 402,which receives the processed feedstock from the feedstock processingsystem 104. The reactor 402 is in fluid communication with an additionalacid source, an oxygen gas source 406, a control gas source 408, and,optionally, a recycled gas source 410. The reactor 402 includes one ormore sensors 412 and an impeller or dispersion device 414. Thetemperature of the reactor 402 is controlled by an energy control system416.

The reactor 402 can have any suitable configuration and be made of anysuitable material. The reactor 402 can be a tank, pipe or tubularreactor. In one embodiment, the reactor 402 is a pipe or tubular reactorthat contains a static mixer to facilitate mixing. In anotherembodiment, the reactor 402 is a pipe that repeatedly changes directionsto facilitate mixing. The reactor 402 can be a batch reactor, plug flowreactor, or continuous stirred-tank reactor. The reactor 402 can be anysuitable size that is capable of accommodating the desired throughput.

The reactor 402 should be made of a material that is chemicallyresistant to the acids 210, 212 and capable of withstanding highpressures. Suitable materials include plastic, titanium alloys,stainless steel, zirconium, and the like. In one embodiment, the reactor402 may be a plastic lined steel vessel (e.g., carbon steel or stainlesssteel lined with polytetrafluoroethylene (PTFE), polyfluoroalkoxy (PFA),or other fluoropolymers). In another embodiment, the reactor 402 can bemade of G-35 stainless steel, or Zirconium 702.

At start-up, the reactor 402 is initially charged with an initialreaction mixture that includes an aqueous solution of the firstoxidizing acid and the second oxidizing acid. In one embodiment, thefirst oxidizing acid is sulfuric acid and the second oxidizing acid isnitric acid. The reactor 402 can be initially charged with an aqueousmixture of sulfuric and nitric acid having any of the concentrationsdescribed above.

In one embodiment, the reactor is a tank reactor. The reactor 402 can befilled to any suitable level with the initial reaction mixture. In oneembodiment, the initial reaction mixture occupies at least approximately25% of the volume of the reactor 402 or, suitably, at leastapproximately 35% of the volume of the reactor 402. In anotherembodiment, the initial reaction mixture occupies no more thanapproximately 80% of the volume of the reactor 402 or, suitably, no morethan approximately 70% of the volume of the reactor 402. In yet anotherembodiment, the initial reaction mixture occupies approximately 25% to80% of the volume of the reactor 402 or, suitably, approximately 35% to70% of the volume of the reactor 402. Preferably, the initial reactionmixture occupies approximately 50% of the volume of the reactor 402. Inany of these embodiments, the remainder of the volume of the reactor402, i.e., the headspace, is occupied by gases.

The headspace is initially charged with oxygen gas and/or one or moreother gases, preferably inert gases. The oxygen gas facilitatesoxidation of the feedstock and/or regeneration of the nitric acid in thereaction mixture as described in greater detail below. The oxygen gas406 may be supplied from any suitable source. For example, the oxygensource can come from air, pure or substantially pure oxygen gas, or eventhe product of another reaction.

In one embodiment, the amount of oxygen gas in the headspace at start-upis at least approximately 2 volume percent, desirably, at leastapproximately 5 volume percent, or, suitably, at least approximately 8volume percent. In another embodiment, the amount of oxygen gas in theheadspace at start-up is no more than approximately 80 volume percent,desirably, no more than approximately 60 volume percent, or, suitably,no more than approximately 55 volume percent. In yet another embodiment,the amount of oxygen gas in the headspace at start-up is approximately 2to 80 volume percent, desirably, 5 to 60 volume percent, or, suitably, 8to 55 volume percent.

The headspace can also be charged with other gases that are inert orotherwise unable to adversely affect the redox reaction. Suitable gasesinclude nitrogen, argon, and the like. In one embodiment, the headspaceis charged with air, which includes a mixture of nitrogen, oxygen, andother gases. These gases are supplied as the control gas 408 in FIG. 4.

At start-up, the temperature and pressure are increased together untiloperating conditions are reached. For example, when the temperaturereaches 60° C., the pressure is increased by adding gas to the headspaceuntil it is approximately 1035 kPa. At 150° C., the pressure isincreased to approximately 2070 kPa. Once the mixture reaches operatingtemperature, the pressure is increased to approximately 3450 kPa. Itshould be appreciated, that the temperature and pressure may fluctuatesubstantially from the initial levels during operation.

The initial reaction mixture is heated by the energy control system 416to at least 150° C. as the impeller 414 vigorously mixes or agitates thereaction mixture. The energy control system 416 includes one or moreheat exchangers positioned inside and/or outside the reactor 402. Itshould be appreciated that the redox reaction is exothermic andcontributes heat to the reactor 402. The energy control system 416 canbe used to heat or cool the reactor 402 and the reaction mixture insidedepending on the circumstances. It should be appreciated that the sameheat exchanger can be used to heat or cool the reactor 402 as desired ormultiple heat exchangers can be used.

It should be appreciated that the energy control system 416 can beviewed as a collection of any number, type, or configuration of heatexchangers, heat sources, heat sinks and other energy transfer devicesand components that add and/or extract heat from various streams,reactors, etc. For example, the energy control system 416 may include asupplemental heat source that is used to supply and/or remove heat fromthe heat exchanger using one or more heat exchange coils.

The gas in the headspace of the reactor may be dispersed into thereaction mixture. This prevents oxygen gas from accumulating in theheadspace. In one embodiment, this is accomplished using an impellerthat propels the gas from the headspace into the reaction mixture as theimpeller rotates. The result is that the composition of the gas in thereaction mixture is close to or the same as the composition of the gasin the headspace. In particular, the concentration of oxygen gas in thedissolved and entrained gas portion of the reaction mixture is similar,if not the same, as the concentration of oxygen gas in the headspace.The reaction mixture may be mixed vigorously to increase the totalamount of oxygen gas in the mixture.

The impeller 414 is used to thoroughly and vigorously mix the reactionmixture and disperse the gas from the headspace into the reactionmixture. The impeller 414 can have any suitable design or configurationso long as it is capable of adequately mixing the gas in the headspacewith the reaction mixture. In one embodiment, the impeller 414 includestwo sets of blades. One set of blades is located at the bottom of theimpeller 414, which is near the bottom of the reactor 402. These bladesare positioned just above the sparger through which oxygen gas isinjected into the reactor 402. The blades shear the oxygen gas to bettermix it into the liquid. Another set of blades is positioned at the topof the reaction mixture. This set of blades propels the gas in theheadspace into the reaction mixture. Both sets of blades are attached toa single shaft.

In another embodiment, the impeller 414 is a gas entrainment impeller.The gas is dispersed by impeller blades attached to a hollow shaftthrough which gases are continuously recirculated from the headspace ofthe reactor 402. The gas enters openings near the top of the shaft andis expelled through dispersion ports located at the tips of the impellerblades. The high speed rotation of the impeller blades creates a lowpressure area at the tip. The pressure at the tip of the blades drops asthe speed of the impeller 414 increases, thereby increasing the rate atwhich gas is dispersed from the headspace through the reaction mixture.

The reactor 402 can also include one or more baffles that enhancedispersion of the headspace gas as well as the general stirring of thereaction mixture. The transfer of gas is governed by the relative speedof the tips of the impeller 414 to the liquid phase, which reduces thepressure at the tips (i.e., creates a vacuum) of the impeller 414 andthereby draws gas into the reaction mixture. A baffle may be used toimpede rotation of the liquid reaction mixture relative to the impeller414. This may enhance the operation of the impeller 414. A baffledesigned specifically for this purpose may be placed in the reactor 402.Alternatively, a cooling/heating coil and/or other structures that areintegral or added to the reactor 402 may function as a baffle. In oneembodiment, the cooling/heating coil has a serpentine shape.

The sensors 412 are used to measure one or more of the followingparameters: temperature, pressure, or liquid level. The sensors 412 canbe used to implement an automated control system or simply provide theoperator with information about the status of the reactor 402.

The reactor 402 may include an emergency blowdown system. In oneembodiment, the emergency blowdown system includes a large-diameter,high pressure pipe that runs from the reactor 402 to an emergencyblowdown containment vessel. In the event of an emergencyoverheat/overpressure situation, the pipe will quickly empty the reactor402 into the emergency blowdown containment vessel. The vessel is sizedto receive all the contents of the reactor 402 without any leaking intothe surrounding environment.

The pressure and/or concentration of the gas in the headspace of thereactor 402 can be adjusted by releasing gas from the headspace. The gascan be released through a gas out port on the reactor 402. A significantamount of the gas exits the reactor 402 through the effluent. In oneembodiment, the ratio of gas that exits through the effluent to gas thatexits in other ways is approximately 0.5 to 1.5.

Once the reactor 402 reaches its operating temperature and pressure, itis ready to receive and oxidize the primary feedstock. The primaryfeedstock is fed into the reactor 402 and shortly thereafter the redoxreaction reaches a steady operating state. At this point, the reactionmixture includes the primary feedstock, the initial start-up oxidizingacids, water, dissolved and entrained gases as well as various reactionproducts. The redox reaction can be indefinitely sustained at a steadystate. Although conditions in the reactor 402 can vary significantlyover time, they do not vary so much that the reaction is adverselyaffected.

In some respects, the start-up parameters of the reactor 402, such asthe oxygen gas concentration in the headspace and the volume occupied bythe reaction mixture, are maintained during operation. For example, theoxygen gas concentrations can be maintained at the levels describedabove during operation. Also, the reaction mixture can occupy the samevolume of the reactor 402 as the initial reaction mixture. Thus, thevolume amounts described above in connection with the initial reactionmixture apply equally to the reaction mixture during operation.

The pressure in the reactor 402 is maintained at a level that issufficient to keep the reaction progressing at a sufficient rate. In oneembodiment, the pressure in the reactor 402 is maintained at at leastapproximately 1035 kPa, desirably, at least approximately 1380 kPa, atleast approximately 1550 kPa, at least approximately 1725 kPa. Inanother embodiment, the pressure in the reactor 402 is maintained at nomore than approximately 6900 kPa, desirably, no more than approximately6200 kPa, or, suitably, no more than approximately 5515 kPa. In yetanother embodiment, the pressure in the reactor 402 is maintained atapproximately 1035 kPa to 6900 kPa, desirably, approximately 1380 kPa to6200 kPa, or, suitably, approximately 1550 kPa to 5515 kPa.

The pressure in the reactor 402 can be maintained by selectively addingoxygen gas 406, control gas 408, or recycled gas 410. If theconcentration of oxygen in the reaction mixture is low, then oxygen gas406 is added. However, if additional oxygen is not needed, then eitherthe control gas 408 or the recycled gas 410 is added. It should beunderstood that the reaction generates gas that also contributes to thepressure inside the reactor 402. Due to the high operating pressure ofthe reactor 402, the oxygen gas 406, the control gas 408, and/or therecycled gas 410 may be supplied at pressures greater than 6900 kPa sothat they will flow into the reactor 402.

The temperature of the reaction mixture is maintained at a level thatprevents the nitric acid from decomposing, but encourages the rapidoxidation of the feedstock. The temperature is controlled with theenergy control system 416 as described above. In one embodiment, thetemperature of the reaction mixture is maintained at no more thanapproximately 210° C. or, desirably, no more than approximately 205° C.In another embodiment, the temperature of the reaction mixture ismaintained at at least approximately 150° C. or, desirably, at leastapproximately 160° C. In yet another embodiment, the temperature of thereaction mixture is maintained at approximately 150° C. to approximately210° C. or, desirably, approximately 160° C. to approximately 205° C.

During operation, the impeller 414 is configured to disperse asufficient amount of the oxygen gas from the headspace into the reactionmixture to facilitate oxidation of the feedstock and/or regeneration ofthe nitric acid. The oxygen can react with the nitric acid reductionproducts to form nitric acid without any processing outside of thereactor. The amount of nitric acid that is regenerated can vary. In oneembodiment, at least a majority of the nitric acid is regenerated,desirably, at least 75% of the nitric acid is regenerated, or, suitablyat least 90% of the nitric acid is regenerated.

The impeller 414 circulates the gas from the headspace through thereaction mixture so that the concentration of the gases in the reactionmixture is very similar to, if not the same as, the concentration of thegases that are dissolved or undissolved in the reaction mixture. Thismakes it possible to control the amount of oxygen gas supplied to thereaction mixture based on oxygen gas measurements taken in theheadspace. In one embodiment, the concentration of dissolved andundissolved oxygen gas in the gaseous portion of the reaction mixture iswithin approximately 25% of the concentration of oxygen gas in theheadspace, desirably, within approximately 10% of the concentration ofoxygen gas in the headspace, or, suitably, within approximately 5% ofthe concentration of oxygen gas in the headspace.

The composition of the gas in the headspace may be adjusted to controlthe reaction products produced by the redox reaction. In one embodiment,the composition of gases inside the reactor meet the followingparameters: oxygen has the concentration given above, carbon dioxide5%-25% by volume; carbon monoxide 2%-10% by volume; nitrous oxide (N2O)2%-5% by volume with the remainder being Argon and/or Nitrogen as wellas minor amounts of NOx and SOx as trace impurities.

The concentration of the oxidizing acids in the reaction mixture are thesame or similar to the concentrations given above. The weight ratios ofsolids to acid or solids to organic material can also be the same orsimilar. Additional acid may be added to the reactor from the additionalacid source or it may be added as part of the mixture that includes thefeedstock.

In one embodiment, the acids 404 can be added directly to the reactor402 and not added to the primary feedstock before it enters the reactor402. In this embodiment, all of the acids are added directly to thereactor 402 in the same or similar amounts and concentrations as givenabove. Adding the acids in this manner lessens the material requirementsfor upstream components (e.g., the mixing vessel 208) because they nolonger need to be capable of withstanding exposure to the acids. Addingthe acids 404 directly to the reactor 402 can also make it easier andfaster to later separate the heavy metals.

Inside the reactor 402, the feedstock undergoes a complex, exothermic,redox process. The organic material in the feedstock reacts to form longand short chain hydrocarbons such as fatty acid alkyl esters, aromatichydrocarbons, complex hydrocarbons, graphitic material, and the like.

An effluent stream can be continually extracted from the reactor 402during operation. The effluent is a runny liquid that includes a liquidfraction (alternatively referred to a liquid component) and a solidfraction (alternatively referred to as a solid component). In oneembodiment, the solid fraction is approximately 2 wt % to approximately10 wt % of the effluent with the rest being the liquid fraction. Theeffluent includes dissolved and entrained gas.

The solid fraction is enriched with carbon containing materials and theliquid fraction is enriched with nitrogen containing materials. In oneembodiment, the weight ratio of carbon to nitrogen in the solidcomponent, on a dry basis, is at least 2, at least 4, at least 6, or atleast 10, times the weight ratio of carbon to nitrogen in the liquidcomponent.

The solid fraction includes hydrocarbon material such as fatty acidesters and non-hydrocarbon material such as fine graphitic material. Thesolid fraction is approximately one third hydrocarbon material and twothirds non-hydrocarbon material. The hydrocarbon material in the solidfraction can include at least 25 wt % fatty acid esters, at least 50 wt% fatty acid esters, or at least 75 wt % fatty acid esters. The fattyacid esters can be mono-alkyl esters of long chain fatty acids(C12-C22).

The hydrocarbon material can include alkyl esters of palmitic acid andstearic acid. In one embodiment, the hydrocarbon material includes atleast approximately 25 wt % of palmitic and stearic acid alkyl esters,at least approximately 35 wt % of palmitic and stearic acid alkylesters, at least approximately 40 wt % of palmitic and stearic acidalkyl esters, at least approximately 45 wt % of palmitic and stearicacid alkyl esters, at least approximately 50 wt % of palmitic andstearic acid alkyl esters, desirably, at least approximately 55 wt % ofpalmitic and stearic acid alkyl esters, or, suitably, at leastapproximately 60 wt % of palmitic and stearic acid esters.

The hydrocarbon material can be used as a biofuel or as an additive fora biofuel. For example, the hydrocarbon material can be used asbiodiesel or as an additive to biodiesel. The non-hydrocarbon materialis carbon rich but takes the form of a fine graphite like material. Thenon-hydrocarbon material can be added to the soil as a supplement thatpromotes plant growth.

The pH of the effluent is the same as the reaction mixture. In oneembodiment, the pH of the effluent is at least approximately 0.5,desirably, at least approximately 0.75, or, suitably, at leastapproximately 0.9. In another embodiment, the pH of the effluent is nomore than approximately 2.0, desirably, no more than approximately 1.75,or, suitably, no more than approximately 1.5. In another embodiment, thepH of the effluent is approximately 0.5 to 2.0, desirably, approximately0.75 to 1.75, or, suitably, approximately 0.9 to 1.5. In anotherembodiment, the pH of the effluent is approximately 1.3.

Upon exiting the reactor 402, the effluent may interact with the energycontrol system 416. The principle purpose of the energy control system416 is to maintain the operating temperature of the reactor 402,although it could also be used to extract usable energy from theprocess. In one embodiment, the effluent passes through a heat exchangerthat transfers heat from the effluent to the feedstock therebypre-heating the feedstock and cooling the effluent. This helps conserveenergy from the reactor 402.

It should be noted that any unreacted nitric acid in the reactoreffluent can be removed by flashing it off before it is cooled below theboiling point of nitric acid. Also, any excess water may be flashed offin the energy control system 416. The need to flash or otherwiseseparate water from the effluent may be reduced by restricting theamount of water that is added to the feedstock.

Turning to FIG. 5, a block diagram of one embodiment of an effluentprocessing system 500 is shown. The effluent processing system 500receives the effluent after it exits the energy control system 416. Anumber of sensors 506 are used to measure parameters such as the pH andconductivity of the cooled effluent. This information is used to controlthe amount of acids 210, 212 that are added to the mixing vessel 208.For example, the lower the pH of the effluent, the less acid 210, 212that needs to be added to the mixing vessel 208.

The cooled effluent flows to the gas separation system 502 where thepressure is reduced to ambient to release the dissolved and entrainedgases. The effluent can be vigorously agitated to facilitate release ofthe dissolved and entrained gases.

The gases can be vented to the atmosphere, recycled back to the reactor402, or separated and captured. If the gases are recycled or separatedand captured, then the gases from the effluent are combined with thegases from the headspace at either the sensors 508 or the gas processingsystem 516. The sensors 508 can be used to measure the oxygenconcentration, temperature, and other parameters. The gas processingsystem 516 can be used to separate the gases. The oxygen and inert gases(argon, nitrogen, and the like) can be recycled back to the reactor 402.Any remaining gas can be moved to the final gas products 518 forventing, storing, packaging, shipping and/or disposal.

The liquid/solids stream from the gas separation system 502 enters thesolids separation system 504 where the solid fraction is separated fromthe liquid fraction so that the liquid fraction can be recycled back tothe feedstock processing system 104. The solids may make it difficult torecycle some of the effluent back to the reactor 402 without clogging orplugging the piping.

The solid fraction can be separated using any of a number of techniquesand/or devices. Examples include mechanical separation techniques anddevices such as a rotary drum vacuum filter, centrifuge, belt filterpress, plate and frame press, vacuum bed, and the like. In oneembodiment, the solids are filtered out of the effluent.

The liquid fraction from the separation system 504 is either recycledback to the feedstock processing system or processed to remove heavymetals in the heavy metal removal system 510. Heavy metals may beseparated from the liquid fraction in a variety of ways. In oneembodiment, the liquid fraction is allowed to sit for a sufficientperiod of time for the heavy metals to precipitate out of the solution.

While not wishing to be bound by theory, it is believed that the heavymetals are held in solution by organic esters such as fatty acid esters.As the esters slowly degrade, the heavy metals precipitate to the bottomof the solution. The heavy metals may also react with the chloride inthe solution to produce heavy metal chloride salts that precipitate outof the solution.

In another embodiment, the heavy metals are removed using an ionexchange material or activated carbon. For example, the liquid fractionis passed through a packed column that contains the ion exchangematerial or the activated carbon. The heavy metals are absorbed by thesematerials to produce a cleaned liquid fraction. In yet anotherembodiment, ferric oxide may be added to the liquid fraction tofacilitate precipitation of the heavy metals. Any combination of thesetechniques may also be used.

The heavy metals removal system 510 may be capable of removing arsenic,cadmium, cobalt, mercury, molybdenum, and/or selenium. In oneembodiment, the heavy metals removal system 510 is capable of removingat least 80 wt % or at least 90 wt % of arsenic, cadmium, cobalt,mercury, molybdenum, and/or selenium. In another embodiment, the heavymetals removal system 510 is capable of removing at least 80 wt % or atleast 90 wt % of arsenic, and/or mercury.

In one embodiment, the heavy metals may be separated using a multistepprocess. For example, the heavy metals can be precipitated out of theliquid effluent, then the remainder of the heavy metals are separatedusing an ion exchange process. The precipitation step removes most ofthe arsenic, cadmium, cobalt, mercury, molybdenum, and selenium whilethe ion exchange process removes chromium and lead.

The cleaned liquid fraction from the heavy metal removal system 510 ismixed with ammonia in the final products processing system 514. Theammonia neutralizes the acids until it reaches a pH that makes itsuitable for use as a fertilizer. The resulting liquid product containsa mixture of organic and inorganic materials that make it a very goodfertilizer.

The amount of ammonia added to the cleaned liquid fraction may varydepending on the relevant soil conditions. For example, if the soil isalkaline, it may be desirable to apply slightly acidic fertilizer toneutralize the soil. In this situation, ammonia is added to bring the pHof the solution up to approximately 4.0 or approximately 4.5. If thesoil is acidic, then it may be desirable to add enough ammonia to createa basic solution.

The solid fraction from the separation system 504 enters another heavymetal removal system 512 where the solid fraction is processed to removemost or all of the heavy metals. It should be appreciated that, in someembodiments, the heavy metal removal system 512 may be the same as theheavy metal removal system 510.

The heavy metals may be removed from the solid fraction in any of anumber of ways. In one embodiment, the heavy metals are removed from thesolid fraction using the cleaned liquid fraction. For example, a portionof the cleaned liquid fraction is mixed with the solid fraction toextract the heavy metals from the solid fraction. The resulting liquidis reprocessed through the heavy metal removal system 510 to isolate andeliminate the heavy metals. In another embodiment, the heavy metals areremoved using a solvent extraction process that is capable of solvatingthe heavy metals.

As described above, the solid fraction can be divided up and used as abiofuel, fertilizer, and/or a soil amendment.

FIG. 6 shows a block diagram of another embodiment of a feedstockprocessing system 600. The sewage material 102 initially enters apreprocessing system 606 where the sewage material 102 is comminuted ina cutter 602 and a grinder 604 positioned in series. The preprocessingsystem 606 can have any of the features described above in connectionwith the preprocessing system 206, including particle size.

The cutter 602 and the grinder 604 are each associated with a tank wherethe sewage material 102 is stored. The sewage material 102 is initiallypumped as a batch into the tank associated with the cutter 602. Thesewage material 102 is circulated through the cutter 602 until itreaches a uniform small size. The sewage material 102 is then pumped asa batch into the tank associated with the grinder 604 where it iscirculated through the grinder 604 until it reaches a uniformconsistency. The sewage material 102 is then pumped into the primaryfeedstock storage 614—e.g., a tank.

It should be appreciated that the configuration of the preprocessingsystem 606 can vary substantially from what is shown in FIG. 6. Forexample, the preprocessing system 606 can include additional processingsteps such as dewatering and the like. Also, the cutter 602 and thegrinder 604 can be combined into a single device that is capable ofcomminuting the sewage material 102 to the desired particle size.

The primary feedstock is pumped out of the primary feedstock storage 216and into a heat exchanger 618 with the feeding device 216. The feedingdevice 216 can be any suitable feeding device including any of thosediscussed above. In a preferred embodiment, the feeding device 216 is ahigh pressure pump with one or more check valves that prevent backflowof the primary feedstock. The feeding device 216 pushes the primaryfeedstock past the check valve using a hydraulic or pneumatic ramconfiguration. The feeding device 216 moves through a cycle where theprimary feedstock is injected through the check valve by extending (orretracting) the ram and is refilled by retracting the ram (or extending)the ram.

The feeding device 216 pressurizes the primary feedstock to the reactionpressures described above. A single device can be used to produce apulsed flow of primary feedstock or two or more devices can bepositioned in parallel to produce a continuous or approximatelycontinuous flow of primary feedstock.

The pressurized primary feedstock passes through the heat exchanger 618where it is heated to the desired reaction temperatures described above.In one embodiment, the primary feedstock is heated to approximately 180°C.

The primary feedstock is heated by the hot reactor effluent and asupplemental heater 624. In the embodiment shown in FIG. 6, heat istransferred from the hot reactor effluent to a fluid 611 in a heatexchanger 620. The fluid 611 can be any suitable fluid such as water,oil, and the like.

The hot reactor effluent provides a significant amount of heat to thefluid 611, but typically it is not enough to heat the primary feedstockto the desired temperature. The fluid 611 is heated further with asupplemental heater 624 and a corresponding heat exchanger 622. Forexample, the heater 624 heats a fluid 613 (water, oil, or the like) thatthen passes through the heat exchanger 622 and heats the fluid 611. Thefluid 611 then passes through the heat exchanger 618 where it heats theprimary feedstock.

It should be appreciated that the heat exchangers 618, 620, 622 can haveany suitable configuration. In one embodiment, the heat exchangers 618,620 are shell and tube heat exchangers and the fluid 611 flows throughthe shell side of the heat exchangers 618, 620. This configuration maybe more efficient than simply using a single heat exchanger where theeffluent flows through the tube side and the primary feedstock flowsthrough the shell side.

The heat exchangers 618, 620, 622 can be made of any suitable material.The heat exchangers 618, 622 are not exposed to acids so they can bemade of common materials such as carbon steel, stainless steel, and thelike. The heat exchanger 620 is exposed to acids in the hot reactoreffluent so it should be made of more robust materials such as titanium,stainless steel (e.g., G-35 stainless steel), zirconium (zirconium 702),and the like.

It should be appreciated that the primary feedstock can be heated usinga variety of additional configurations. For example, in one embodiment,the primary feedstock can be heated with the supplemental heater 624without involving the hot reactor effluent. In another embodiment, theheat exchangers 618, 620 can be combined so that the hot reactoreffluent and the primary feedstock pass through a single heat exchangermaking the fluid 611 unnecessary. Numerous other changes can be made aswell.

The primary feedstock is now at the desired reaction pressure andtemperature and is ready to be fed into the reaction system 700 shown inFIG. 7. The reactor 702 can be any of the reactors described above inconnection with reactor 402. In a preferred embodiment, the reactor 702is a pipe or tubular reactor made of plastic lined steel, e.g., carbonsteel or stainless steel lined on the inside withpolytetrafluoroethylene (PTFE), polyfluoroalkoxy (PFA), or otherfluoropolymers. The pipe includes multiple curves or elbows thatfacilitate mixing of the reaction mixture as it flows through the pipe.

The first oxidizing acid 210, second oxidizing acid 212, and the oxygengas 406 can be added in any suitable configuration or order. In oneembodiment, the components are added to the reactor 702 in the followingorder: the second oxidizing acid 212 is added first, the first oxidizingacid 210 is added second, and the oxygen gas 406 is added last (or addedin multiple locations downstream of the acids 212, 210). In otherembodiments, the acids 210, 212 and oxygen 406 can be added at the sametime or in any other order.

The reaction mixture is formed as soon as any oxidizing acid is added tothe primary feedstock. The dwell time of the reaction mixture in thereactor 702 is sufficient for the sewage material 102 to react to formthe products described above. In general, lower quantities of acids 210,212 and/or oxygen gas 406 increases the dwell time necessary to producethe desired reaction products and vice versa. In one embodiment, thereaction mixture 702 has a dwell time of approximately 10 seconds to 2minutes or 45 seconds to 1 minute.

The concentration of the reaction mixture can be the same as that givenabove in connection with the reactor 402. It should be appreciated thatany other characteristics of the reactor 402 can apply equally to thereactor 702.

The extent of the reaction can be monitored by measuring the temperatureof the reactor 702 at various points. The reaction is exothermic so thetemperature of the reaction mixture should increase as it moves throughthe reactor 702. The difference in temperature from the beginning of thereactor 702 to the end can be used to determine the extent of thereaction.

The hot effluent leaves the reactor 702 and is immediately cooled in theheat exchanger 620 (FIG. 6). The pressure is also reduced soon after theeffluent exits the reactor 702 (e.g., a valve is used to reduce thepressure). The reaction is effectively terminated when the reactionmixture is cooled and the pressure is released.

The reactor effluent leaves the heat exchanger 620 and enters a effluentprocessing system 800 as shown in FIG. 8. The solids are separated fromthe liquid in the solids separation system 504. The heavy metals areremoved from the liquid in the heavy metal removal system 510, and theheavy metals are removed from the solids in the heavy metal removalsystem 512. The clean liquid (after heavy metal removal) is thenprocessed in the final products processing system 514. The systems 504,510, 512, 514 operate in the same or similar manner as described above.

The aqueous phase oxidation process 100 can be controlled using avariety of methods. In one embodiment, the process 100 can be monitoredand controlled remotely using various wired and/or wirelesscommunication systems. The process 100 can include sensors that monitorthe various material levels, flows, temperatures, pressures, and anyother parameters associated with the process 100. The informationobtained from the sensors can be transmitted to a remote location wherean operator can control the various parameters of the system 100.

In one embodiment, the information from the process 100 is stored on aserver and made available through a website. The website can be used toaccess the data about the process 100 and to control the process 100.For example, an operator can use the website to remotely increase theamount of oxygen gas added to the reaction mixture or increase the feedrate of the feedstock. Any of the parameters described above inconnection with the process 100 can be controlled through the website.

A separate website or login credentials can be provided to view thevarious parameters of the process 100 without the ability to change orotherwise control the process 100. This can be useful to allow the ownerof a waste disposal site where the process 100 is being used to monitorthe parameters of the process 100 without having the ability to changeor alter it.

In another embodiment, the physical components used in the process 100can be organized into a modular design that makes it easier totransport, set-up, and operate. For example, the various components canbe organized into different skids that can be easily transported andinstalled at a waste processing site. The skids can each be aself-contained unit that fits in or on a semi-trailer—e.g., the skidsare no more than approximately 8 feet wide to allow them to fit on thesemi-trailer. The skids are capable of being loaded and unloaded fromwith a conventional forklift.

In one embodiment, the physical components can be divided into thefollowing skids: feedstock preparation skid, reactor skid, separationsskid, and support skid. The feedstock preparation skid can include thosecomponents that are roughly associated with the feedstock processingsystem 104. This can include raw feedstock storage tank, comminutingcomponents such as the grinder/cutter, dewatering equipment, primaryfeedstock storage tank, pumps, and so forth.

The reactor skid can include those components that are roughlyassociated with the reaction system 106. This can include the reactor,heat exchangers, process control equipment, acids, and the like. Theprocess control equipment can include pneumatic controls housed in anenclosed cabinet at one end of the skid and software and electronicshoused in a second cabinet at the other end of the skid.

The separations skid can include those components that are roughlyassociated with the effluent processing system 108. This can includeseparation devices such as filters, settling tanks and the like, storagetanks, and so forth.

The support skid includes additional components that may be needed torun the process 100. This can include things like a generator, acompressor, a heater (to heat the primary feedstock or to just heat theskids during the winter), and the like.

The skids can be monitored and tracked using various asset managementsystems and techniques. For example, the skids can be individuallytracked using wireless/GPS sensors included on the skids. Also, theskids can be monitored and controlled remotely as described above.

It should be appreciated that the number and content of the skids can bechanged. Also, some materials can be provided outside of a skid. Forexample, the acids may be stored separately from any of the skids incontainment vessels. This prevents the acid from doing any significantdamage if it accidentally spills.

EXAMPLES

The following examples are provided to further illustrate the disclosedsubject matter. They should not be used to constrict or limit the scopeof the claims in any way.

Example 1

In this example, sewage was processed to produce fertilizer and/orotherwise treat the sewage to render it suitable to be discharged intothe environment. The sewage was obtained from a sewage treatment plantand contained 5.2 wt % solids with the rest being almost entirely water.The solid particles in the sewage were suspended in the liquid so thatthe texture of the sewage resembled a readily pourable slurry.

The sewage was dewatered by mixing 75.71 liters of sewage with 1 literof a flocculant solution and agitating the mixture until the solidparticles in the sewage clustered or clumped together. The flocculantsolution contained 10 ml of Core Shell 71307 cationic flocculant and 990ml of water. The Core Shell 71307 flocculant was obtained from the NalcoCompany located in Naperville, Ill.

The liquid was separated from the mixture to yield 19.543 kg ofdewatered sewage. The dewatered sewage contained 20.2 wt % solidmaterial and the rest was water. It had a soft moldable texture. Thedewatered sewage was fed into a reactor in the following manner.

The reactor was initially filled with a liquid mixture that included1,000 ml water, 30 ml aqueous nitric acid solution (54 wt % acid), and15 ml aqueous sulfuric acid solution (93 wt % acid). The pH of theliquid in the reactor was 1.0. The reactor was heated to about 180° C.and pressurized to about 4,826 kPa.

The headspace of the reactor was filled with 50% oxygen gas by volume.The reactor included a gas entrainment impeller that dispersed theheadspace gases into the reaction mixture. The pressure was maintainedby adding oxygen gas or air. Air was added unless the oxygenconcentration in the headspace was low, then oxygen was added. If thepressure was high, gas was released from a valve at the top of thereactor.

During the start-up phase of the process, the dewatered sewage was mixedwith an acid solution in a blender to produce a mixture having a pH of1.0. The blender was used to comminute the solids in the feedstock tomake it uniform. The feedstock included 175 gm dewatered sewage, 450 mlwater, 15 ml aqueous nitric acid solution (54 wt % acid), and 7.5 mlaqueous sulfuric acid solution (93 wt % acid). This was fed into thereactor until it began to produce a steady stream of effluent material.

The process transitioned to a steady state phase when there wassufficient effluent produced to recycle a portion of it back to thebeginning. The recycled effluent was added to the feedstock in place ofthe water that was used during the start-up phase. The amount of acidsadded to the feedstock was lowered since the effluent contained someacid. Enough acid was added, however, to bring the feedstock to a pH of1.0. The result was that the feedstock included 175 gm dewatered sewage,450 ml of recycled effluent (pH approximately 1.3), 10 ml aqueous nitricacid solution (54 wt % acid), and 4 ml aqueous sulfuric acid solution(93 wt % acid). The temperature of the recycled effluent was 50 to 70°C.

The feedstock entered the reactor through two hydraulic rams that werealternately isolated from the high pressure reactor using valves. Thevalve between one hydraulic ram and the reactor was opened to allow theram to feed the feedstock into the reactor while the valve between theother ram and the reactor was closed to allow it to be reloaded withoutdepressurizing the reactor. This made it possible to feed a continuoussupply of feedstock to the reactor without depressurizing the reactor.

The effluent was a runny liquid mixture that contained a significantamount of solids and had a steady state pH of 1.3. The solids had atendency to clump together and/or stick to the equipment, which made itdifficult to process.

The effluent also contained a significant amount of dissolved and/orentrained gas. Approximately half of the gas released by the reactor wasdissolved and/or entrained in the effluent. The other half exited thereactor through a bleed off valve at the top of the reactor. The amountof gas that exited through the effluent was 775 liters and the amount ofgas that exited through the valve at the top of the reactor was 780liters. The gas that exited through the top of the reactor included gasthat was released to reduce the pressure in the reactor and gas that wasslowly released across an oxygen sensor that was used to monitor theoxygen concentration in the reactor.

After exiting the reactor, the effluent was cooled and the pressure wasreduced to atmospheric pressure. This released much of the dissolved andentrained gas, which was then collected. The degassed effluent was thensubjected to vacuum filtration to separate the liquid from the solids.

The filtered liquid was divided and a portion was recycled back to thebeginning of the process as described above. The remaining liquid wasmixed with an aqueous ammonia solution (24% ammonia) until the pH of thesolution reached 4.5. The ammonia reacted with the acids in the effluentto produce ammonium salts that can be used as fertilizer.

Table 1 below shows the composition of the feedstock, liquid effluent,and solid effluent. The composition of the liquid effluent was testedbefore ammonia was added. The composition was determined using EPAmethods 3050A (digestion) and 6010 (determination).

TABLE 1 Effluent composition Minimum Effluent Detectable FeedstockEffluent Solids Level (MDL) (mg/kg) Liquids (mg/kg) (mg/kg) (dry basis)(mg/kg) (dry basis) Heavy Metals Arsenic 0.76 12.5 3.0 19.0 Cadmium 0.142.5 1.0 4.9 Chromium 0.13 22.1 19.6 238.5 Cobalt 0.22 1.0 0.5 1.9 Copper0.39 86.7 34.7 171.8 Mercury 0.003 — .016 — Molybdenum 0.15 3.2 1.1 27.5Nickel 0.31 9.2 13.9 65.0 Lead 2.31 10.5 <MDL 72.8 Selenium 1.12 0.5<MDL 2.9 Zinc 0.54 137.5 67.3 172.2 Plant Nutrients Total Nitrogen 578,269 12,579 9,725 Atoms Phosphorous 3.6 2,559 627 10,750 Phosphorous —5,886 1,441 24,725 Pentoxide (P205) Potassium 29.6 382 113 797 Potassium— 458 135 956 Oxide (K20) Sulfur 10.6 1,913 7,199 54,220 Calcium 12.56,415 640 51,210 Magnesium 4.2 678 315 975 Iron 64.3 1,821 192 13,090Manganese 1.8 22 11 41.3 Boron 0.12 6.1 0.5 40.2 Sodium 13.2 726 2921,058 Chloride 0.75 824 404 225 Total Carbon 30 97,500 30,300 290,500Atoms Carbon/ — 11.79 2.41 29.87 Nitrogen Ratio

The process conditions were such that the dewatered sewage reacted toproduce valuable products. The types of acids used and the relativeconcentrations of each were sufficient to oxidize the sewage to producevaluable products, but not so much that the sewage was completelyoxidized to carbon dioxide, nitrogen gas, and water. For example, theprocess would produce fewer desirable reaction products if greateramounts of nitric acid were used.

The effluent can be used as a fertilizer and/or other soil amendment.The liquid effluent may be sprayed on the soil as a liquid fertilizerand the solid effluent may be spread on or worked into the soil. The pHof the liquid effluent may be adjusted depending on the condition of thesoil. For example, the pH may be somewhat acidic if the liquid effluentwill be applied to alkaline soil. In the alternative, the pH may beadjusted to be basic if the liquid will be applied to acidic soil.

The process was run for ten hours and consumed approximately 7920 gm ofdewatered sewage, 475 ml of aqueous nitric acid (54 wt % acid), 143.5 mlof aqueous sulfuric acid solution (93 wt % acid), and 1,040 liters ofoxygen gas. The process produced approximately 9,060 ml of liquideffluent and 474 gm of solids (on a dry basis). A minor amount ofeffluent remained in the process equipment and was not included in thepreceding amounts. The process also produced 1,555 liters of gas.Approximately half of the gas exited the reactor through the headspaceand the other half was dissolved or entrained in the effluent.

The temperature and pressure in the reactor fluctuated somewhatdepending on the reaction conditions. During the steady state phase ofthe process, the temperature in the reactor was maintained atapproximately 180° C. although it fluctuated at times from 150° C. to200° C. The pressure in the reactor was maintained at approximately4,826 kPa plus or minus 200 kPA.

Example 2

In this example, various methods and materials were tested for removingheavy metals from the liquid effluent. The tests were especially focusedon removing heavy metals such as arsenic, cadmium, chromium, mercury,lead, and selenium. The other heavy metals tested are either of lessconcern or may even be considered micronutrients.

The liquid effluent was prepared using the method described in Example 1and divided into six samples. The samples were processed as follows. InSample 1, the liquid effluent was allowed to sit undisturbed in a flaskfor about a month. The heavy metals separated to the bottom of the flaskand the remaining liquid was drawn off the top. In Samples 2-5, theliquid effluent was mixed with the hydrated ion exchange beads shown inTable 2. In each sample, 100 ml of liquid effluent was mixed with 1 gmof ion exchange beads and gently shaken. In Sample 6, 100 ml of liquideffluent was mixed with 1 gm of ferric oxide (Fe₂O₃) and gently shaken.The composition of the resulting liquid from each sample was thentested.

TABLE 2 Ion exchange beads Sample Ion Exchange Beads Sample 2XUR-1525-L10-018 from the Dow Chemical Company Sample 3 XUR-1525-L10-019from the Dow Chemical Company Sample 4 XUR-1525-L10-020 from the DowChemical Company Sample 5 XUR-1525-L10-021 from the Dow Chemical Company

The composition of the liquid samples produced from each test are shownin Table 3. One notable result is Sample 1. The passive precipitationprocess removed arsenic, cadmium, mercury, and selenium to levels thatare undetectable. While not wishing to be bound by theory, it isbelieved that the heavy metals form a complex with organic esters thatkeep the heavy metals in solution. The esters break down over timecausing the heavy metals to drop out of solution. The ion exchange beadsused in Sample 5 show promise for removing the chromium and lead fromthe liquid effluent. It should also be noted that the plant nutrientswere not significantly affected in any of the tested samples.

TABLE 3 Heavy metal removal Sample MDL Sample 1 Sample Sample SampleSample Sample (mg/kg) 1 (precip) 2 3 4 5 6 Heavy Metals Arsenic 0.76<MDL 14.7 <MDL <MDL <MDL <MDL <MDL Cadmium 0.14 <MDL <MDL <MDL <MDL <MDL<MDL <MDL Chromium 0.13 14.9 18.2 13.9 10.8 10.7 9.8 11.9 Cobalt 0.22<MDL <MDL <MDL <MDL <MDL <MDL <MDL Copper 0.39 32.7 78.9 32.2 28.5 27.127.2 28.4 Mercury 0.003 <MDL 18.313 <MDL <MDL <MDL <MDL <MDL Molybdenum0.15 <MDL 41.8 <MDL <MDL <MDL <MDL <MDL Nickel 0.31 11.0 2.9 11.2 11.211.1 10.8 11.0 Lead 2.31 3.4 82.8 4.0 4.0 3.9 3.6 3.2 Selenium 1.12 <MDL41.4 <MDL <MDL <MDL 1.3 3.4 Zinc 0.54 64.0 15.1 50.0 65.0 64.4 62.4 58.1Plant Nutrients Total 57 11,643 3,989 12,296 12,350 12,257 12,058 12,529Nitrogen Atoms Phosphorous 3.6 525 522 364 476 484 405 368 Phosphorous —1,207 1,200 837 1,095 1,113 932 847 Pentoxide (P205) Potassium 29.6 11441 113 126 112 104 114 Potassium — 136 49 135 151 135 124 136 Oxide(K20) Sulfur 10.6 6,698 181,500 6,572 6,530 6,708 6,547 6,721 Calcium12.5 576 192,800 492 455 450 436 1,203 Magnesium 4.2 303 89 295 310 307298 366 Iron 64.3 122 633 86 81 93 53 102 Manganese 1.8 4.0 <MDL 2.1 4.03.9 3.5 8.9 Boron 0.12 0.9 3.5 0.9 0.9 0.9 0.7 0.9 Sodium 13.2 271 107271 277 273 265 275 Total Carbon 30 28,900 54,700 29,700 28,900 28,50029,600 29,700 Atoms Carbon/Nitrogen — 2.48 13.71 2.42 2.34 2.33 2.452.37 Ratio

Example 3

In this example, the composition of the solid organic materials producedby the process was tested. The sewage was obtained and dewatered in themanner described in Example 1 except that it was dewatered to 17 wt %solid content. The reactor was initially filled with a liquid mixturethat included 1,450 recycled effluent having a pH of 1.3 (from aprevious run), 8.5 ml aqueous nitric acid solution (54 wt % acid), and21.5 ml aqueous sulfuric acid solution (93 wt % acid). The pH of theliquid in the reactor was 1.0. The reactor was heated to about 180° C.and pressurized to about 4,826 kPa.

The headspace of the reactor was filled with 50% oxygen gas by volume.The reactor included a gas entrainment impeller that dispersed theheadspace gases into the reaction mixture. The pressure was maintainedby adding oxygen gas or air. Air was added unless the oxygenconcentration in the headspace was low, then oxygen was added. If thepressure was high, gas was released from a valve at the top of thereactor.

The dewatered sewage was mixed with the recycled liquid fraction of theeffluent (if this was at start-up, the recycled liquid fraction wasobtained from a previous run) in a blender to produce a mixture having apH of 1.0. The blender was used to comminute the solids in the feedstockto make it uniform. The feedstock included 175 gm dewatered sewage, 450ml recycled liquid effluent, 3.5 ml aqueous nitric acid solution (54 wt% acid), and 9.0 ml aqueous sulfuric acid solution (93 wt % acid). Thiswas fed into the reactor.

The feedstock entered the reactor through two hydraulic rams that werealternately isolated from the high pressure reactor using valves. Thevalve between one hydraulic ram and the reactor was opened to allow theram to feed the feedstock into the reactor while the valve between theother ram and the reactor was closed to allow it to be reloaded withoutdepressurizing the reactor. This made it possible to feed a continuoussupply of feedstock to the reactor without depressurizing the reactor.

The effluent was a runny liquid mixture that contained a significantamount of solids and had a steady state pH of 1.3. The solids had atendency to clump together and/or stick to the equipment, which made itdifficult to process.

The effluent also contained a significant amount of dissolved and/orentrained gas. Approximately half of the gas released by the reactor wasdissolved and/or entrained in the effluent. The other half exited thereactor through a bleed off valve at the top of the reactor. The amountof gas that exited through the effluent was 775 liters and the amount ofgas that exited through the valve at the top of the reactor was 780liters. The gas that exited through the top of the reactor included gasthat was released to reduce the pressure in the reactor and gas that wasslowly released across an oxygen sensor that was used to monitor theoxygen concentration in the reactor.

After exiting the reactor, the effluent was cooled and the pressure wasreduced to atmospheric pressure. This released much of the dissolved andentrained gas, which was then collected. The degassed effluent was thensubjected to vacuum filtration to separate the liquid from the solids.

The filtered liquid was divided and a portion was recycled back to thebeginning of the process as described above. The remaining liquid wasmixed with an aqueous ammonia solution (24% ammonia) until the pH of thesolution reached 4.5. The ammonia reacted with the acids in the effluentto produce ammonium salts that can be used as fertilizer.

The organic materials in the solid component of the effluent wereextracted using a solvent and analyzed. The results are shown in Table 4below. The materials listed in Table 4 represent 93% of the amount ofthe total organic materials identified. The remaining 7% are not listeddue to their low concentrations.

TABLE 4 Composition of the organics in the solid component of theeffluent Material Wt % Material Wt % Methyl palmitate 34.6658-Octadecenoic acid, 1.137 (Hexadecanoic acid, methyl ester methylester) Methyl stearate 27.541 8,11-Octadecadienoic 0.758 (Octadecanoicacid, acid, methyl ester methyl ester) Methyl myristate 5.954 Methyl14-methylpalmitate 1.283 (Tetradecanoic acid, (14-methylhexadecanoicmethyl ester) acid, methyl ester) Methyl oleate 4.973 Dimethyl azelate0.379 ((Z)-9-Octadecenoic (Nonanedioic acid acid, methyl ester) dimethylester) Methyl pentadecanoate 3.201 Methyl caprate 0.357 (Pentadecanoic(Decanoic acid, acid, methyl ester) methyl ester) Octadecanoic acid,2.576 3-Hydroxyoctadecanoic 0.357 10-oxo-, methyl ester acid, methylester Methyl icosanoate 2.241 Methyl isopalmitate 0.335 (Eicosanoicacid, (14-Methylpentadecanoic methyl ester) acid, methyl ester) Methyllaurate 1.862 3-Hydroxydodecanoic 0.323 (Dodecanoic acid, acid, methylester methyl ester) Methyl heptadecanoate 1.438 Dodecyl alcohol 0.312(Heptadecanoic acid, (1-Hydroxydodecane) methyl ester) Methyldocosanoate 1.427 Linolelaidic acid, methyl 0.301 (Docosanoic acid,ester (delta 9-trans 12-trans methyl ester) Octadecadienoic acid, methylester) 12-Methyltetradecanoic 1.249 Methyl benzoate 0.290 acid, methylester Total 93%

The results show that the organic materials in the solid fraction of theeffluent are primarily made up of mono-alkyl esters of long chain fattyacids (C12-C20). These materials are valuable and can be used forbiodiesel, biolubricants, and the like. The liquid fraction of theeffluent included a de minimis amount of organic material.

Example 4

In this example, the process was run a number of times using onlysulfuric acid and one time using a mixture of sulfuric and nitric acid.The run with nitric acid was used for comparison purposes with the otherruns. The feed material was sewage material obtained from a sewagetreatment plant. The sewage material included approximately 4.5% to 5.5%solids with the rest being almost entirely water. The solid particles inthe sewage were suspended in the liquid so that the texture of thesewage resembled a readily pourable slurry. The sewage material was notdewatered, but it was comminuted in a blender to make the solids roughlyuniform in size.

Each run was performed as a batch run. The reactor was heated to about180° C. and pressurized to about 5515 kPa. The sewage material was mixedwith the acid and then fed into the reactor using a hydraulic ram. ThepH of the mixture just before entering the reactor was 1.0. The amountof each material is shown in Table 5 below.

TABLE 5 Run parameters Sulfuric Nitric Acid (mL) Acid (mL) Re- Feed (93wt (54 wt Pressure Temp pH of action (mL) % acid) % acid) (kPa) (C.)Effluent time Run 1 1300 4.5 0 5515 180 1.3 24 Run 2 1300 12 0 5515 1801.3 18 Run 3 1150 9 6 5515 180 1.3 8 Run 4 1150 12 0 5515 180 1.3 18

Oxygen gas was bubbled into the reactor at a rate of 1.5 L/min for theduration of the reaction. The concentration of oxygen in the reactor wasnot measured, but the amount that was added ensured that it was anoxygen rich environment. The oxygen gas entered the reactor through asparger positioned at the bottom of the reactor. The reactor included animpeller that rotates and creates a vortex which draws the gas from theheadspace down into the reaction mixture. The pressure was maintained atthe desired level by adding air to the reactor or releasing gas from theheadspace.

The results showed that the effluent from the run that included nitricacid is preferable to effluent from the runs that included only sulfuricacid. The effluent from the sulfuric only runs had cellulosic materialin it and larger particle sizes. The large particle sizes made it easierto filter the solids from the effluent, but the presence of cellulosicmaterial was a drawback. The effluent from the run that included nitricacid was a runny liquid mixture that contained a significant amount ofsmall particle solids and very little, if any, cellulose material. Theorganic material was broken down further by the nitric acid making itbetter suited for use as a soil amendment or biofuels.

The nitric acid also increased the reaction rate and throughput of thereactor as shown by the reaction times given in Table 5. The nitric acidresulted in a more complete reaction as evidenced by the texture andphysical properties of the effluent and did so in less than half thetime of the sulfuric acid only runs. The faster reaction time wasreflected in the amount of heat produced by each run. The nitric acidrun produced significantly more heat in less time than the sulfuric acidruns.

Example 5

In this example, sewage was processed in a continuous tubular reactor toproduce fertilizer and/or otherwise treat the sewage to render itsuitable to be discharged into the environment. The sewage was obtainedfrom a sewage treatment plant and contained approximately 5.5 wt %solids with the rest being almost entirely water. The solid particles inthe sewage were suspended in the liquid so that the texture of thesewage resembled a readily pourable slurry.

The sewage was processed in a cutter and then a grinder to reduce thesize of the solid particles and provide the sewage with a uniformparticle size distribution. The sewage was not dewatered. The sewage wasfed into a heat exchanger and later a reactor in by a Williams pump, anair driven cylinder that pressurized the sewage to approximately 2070kPa. A single pump was used that created a pulsed flow—i.e., the sewageflowed when the cylinder was pushing sewage, but no sewage flowed whenthe sewage was being refilled.

The sewage was heated in the heat exchanger to approximately 180° C. Thesewage was on the shell side of the heat exchanger and heated water wason the tube side of the heat exchanger. The water was heated by passingit through a heat exchanger with the hot effluent from the reactor andanother heat exchanger supplied with hot oil from an external heater.

The heated and pressurized sewage then entered the reactor where it wasmixed with nitric acid, sulfuric acid, and oxygen gas. The reactor was aone inch carbon steel pipe lined with polytetrafluoroethylene (PTFE).The pipe included multiple turns and changes of direction to help mixthe reaction mixture as it passed through the pipe. Nitric acid wasadded to the feedstock first followed by sulfuric acid. Oxygen gas wasadded last.

When the reaction mixture reached the end of the reactor, the pipe wasinitially cooled with a fan or a water cooling system. The effluentpassed through a valve that lowered the pressure to close to atmosphericpressure. The effluent then passed through the previously mentioned heatexchanger. The effluent was then processed to separate the solids,remove heavy metals, and neutralize any residual acids.

Multiple runs were performed in this manner using different amounts ofacids and/or oxygen. Runs 1-4 explore how the amount of acid affects thereaction and runs 5-7 explore how the amount of oxygen gas affects thereaction. The parameters for each run are shown below in Table 6.

TABLE 6 Run parameters Sulfuric Nitric Feed- Re- Feed Acid Acid stockaction Temp (mL/ (mL/min) (mL/min) Oxygen Temp Temp change min) (93%)(54%) (L/min) (C.) (C.) (C.) Run 1 720 6.08 3.44 Not measured 176 172 −4Run 2 720 7.6 4.3 Not measured 176 177 1 Run 3 720 8.36 4.73 Notmeasured 176 180 4 Run 4 800 5.32 2.58 Not measured 179 183 4 Run 5 200022.8 12.9 16 169 173 4 Run 6 2000 23.56 14.19 20 170 173 3 Run 7 200024.32 12.9 6 172 181 9

Run 1 produced very little reaction with a drop in the temperature. Theeffluent was chunky, which indicated that it hadn't completely reacted.Run 1 likely could have benefitted from additional acid. Run 2 produceda small reaction with a small temperature rise. The effluent was stillchunky. Run 2 likely could also have benefitted from additional acid.

Run 3 produced a good reaction with a good temperature rise. Theeffluent did not contain any chunks. This run had enough acid to oxidizethe sewage material the desired amount. Run 4 began with higher acidlevels until all of the process equipment was up to temperature. After afew hours the acid levels were lowered to the amount shown and a goodreaction with a good temperature rise was still obtained. The effluentdid not contain any chunks.

Runs 5-7 all produced a good reaction with a good temperature rise.However, the effluent in runs 5-6 was foamy and gelatin like and thesolid particles would not settle. The additional acid in run 6 did notnoticeably change the effluent. The effluent in run 7 was not foamy,chunky, or gelatin like and the solid particles settled out readily. Theexcess oxygen gas seems to be the cause of the less desirable effluentin runs 5-6.

It should be understood that although certain results are expressed asbeing more or less desirable, those results that are characterized asbeing less desirable are still a substantial improvement over existingsewage processing technology. Thus, the less desirable results can stillbe desirable in many situations.

ILLUSTRATIVE EMBODIMENTS

Reference is made in the following to a number of illustrativeembodiments of the disclosed subject matter. The following embodimentsillustrate only a few selected embodiments that may include one or moreof the various features, characteristics, and advantages of thedisclosed subject matter. Accordingly, the following embodiments shouldnot be considered as being comprehensive of all of the possibleembodiments.

The concepts and aspects of one embodiment may apply equally to one ormore other embodiments or may be used in combination with any of theconcepts and aspects from the other embodiments. Any combination of anyof the disclosed subject matter is contemplated.

In one embodiment, a method comprises feeding waste material into areactor that includes a reaction mixture, the waste material being atleast part of the reaction mixture. The waste material is reacted withsulfuric acid in the reactor and the reaction mixture includes no morethan approximately 7.5 wt % acid.

In another embodiment, the method comprises feeding waste material intoa reactor and reacting the waste material with sulfuric acid in thereactor to produce an effluent. The effluent includes a solid componentand a liquid component and the weight ratio of carbon to nitrogen in thesolid component, on a dry basis, is at least two times the weight ratioof carbon to nitrogen in the liquid component.

In another embodiment, the method comprises reacting waste material withan oxidizing acid in a reactor to produce a first effluent, separatingsolids from the first effluent to produce a liquid effluent, andseparating heavy metals from the liquid effluent.

The waste material may be any organic waste material. The waste materialcan have an organic content of at least 25 wt %, at least 50 wt %, or atleast 75 wt % on a dry basis. The waste material can include sewagematerial such as dewatered sewage, sewage sludge, farm animal waste, orfruit and vegetable waste such as potato skins and the like. The wastematerial may be combined with recycled effluent from the reactor beforethe waste material enters the reactor. Additional acid may be combinedwith the waste material and recycled effluent before the waste materialenters the reactor.

The acid may be combined with the waste material before the wastematerial enters the reactor. A portion of the effluent from the reactormay be recycled back to the reactor. The sulfuric acid and/or nitricacid may be combined with the waste material and/or recycled effluentbefore the waste material enters the reactor. The temperature in thereactor may be maintained at no more than approximately 210° C. and thepressure in the reactor may be maintained at at least 2070 kPa or atleast 2800 kPa. The gas in the headspace of the reactor may be dispersedinto the reaction mixture with an impeller or like device.

Oxygen gas may be supplied to the reactor to further facilitate thereaction. The concentration of dissolved and entrained gas in thegaseous portion of the reaction mixture may be maintained withinapproximately 25% of the concentration of oxygen gas in the headspace ofthe reactor. The gas in the headspace of the reactor may comprise atleast 25 volume percent oxygen gas or at least 40 volume percent oxygengas.

The solids may be separated from the effluent to produce a liquideffluent. The solids may be separated from the effluent by filtering theeffluent. The heavy metals may be separated from the liquid component ofthe effluent. At least approximately 80 wt % of arsenic, cadmium,cobalt, mercury, molybdenum, and/or selenium may be separated from theliquid component of the effluent.

The reaction mixture may include an oxidizing acid such as sulfuric acidand/or nitric acid. The reaction mixture may include no more thanapproximately 5 wt % acid or no more than approximately 3 wt % acid. Thereaction mixture may include no more than approximately 5 wt % sulfuricacid or no more than approximately 3 wt % sulfuric acid. The reactionmixture may include sulfuric acid, nitric acid, or some other oxidizingacid. The weight ratio of sulfuric acid to nitric acid can at leastapproximately 0.5, at least approximately 0.75, at least approximately1, or at least approximately 1.5. The pH of the reaction mixture may beapproximately 0.5 to 2.0, approximately 0.75 to 1.75, or approximately0.9 to 1.5.

The heavy metals may be separated form the liquid effluent byprecipitating the heavy metals from the liquid effluent. The heavymetals can also be separated form the liquid effluent by contacting theliquid effluent with an ion exchange material or activated carbon. Theheavy metals can also be separated from the liquid effluent by addingferric oxide to the liquid effluent. The solids can be separated fromthe first effluent by filtering the effluent.

At least approximately 80 wt % or approximately 90 wt % of arsenic,cadmium, cobalt, mercury, molybdenum, and/or selenium may be separatedfrom the liquid effluent. The weight ratio of carbon to nitrogen in thesolid component, on a dry basis, may be more than four times, fivetimes, or six times the weight ratio of carbon to nitrogen in the liquidcomponent.

The terms recited in the claims should be given their ordinary andcustomary meaning as determined by reference to relevant entries inwidely used general dictionaries and/or relevant technical dictionaries,commonly understood meanings by those in the art, etc., with theunderstanding that the broadest meaning imparted by any one orcombination of these sources should be given to the claim terms (e.g.,two or more relevant dictionary entries should be combined to providethe broadest meaning of the combination of entries, etc.) subject onlyto the following exceptions: (a) if a term is used in a manner that ismore expansive than its ordinary and customary meaning, the term shouldbe given its ordinary and customary meaning plus the additionalexpansive meaning, or (b) if a term has been explicitly defined to havea different meaning by reciting the term followed by the phrase “as usedherein shall mean” or similar language (e.g., “herein this term means,”“as defined herein,” “for the purposes of this disclosure the term shallmean,” etc.).

References to specific examples, use of “i.e.,” use of the word“invention,” etc., are not meant to invoke exception (b) or otherwiserestrict the scope of the recited claim terms. Other than situationswhere exception (b) applies, nothing contained herein should beconsidered a disclaimer or disavowal of claim scope.

The subject matter recited in the claims is not coextensive with andshould not be interpreted to be coextensive with any particularembodiment, feature, or combination of features shown herein. This istrue even if only a single embodiment of the particular feature orcombination of features is illustrated and described herein. Thus, theappended claims should be given their broadest interpretation in view ofthe prior art and the meaning of the claim terms.

As used herein, spatial or directional terms, such as “left,” “right,”“front,” “back,” and the like, relate to the subject matter as it isshown in the drawings. However, it is to be understood that thedescribed subject matter may assume various alternative orientationsand, accordingly, such terms are not to be considered as limiting.

Articles such as “the,” “a,” and “an” can connote the singular orplural. Also, the word “or” when used without a preceding “either” (orother similar language indicating that “or” is unequivocally meant to beexclusive—e.g., only one of x or y, etc.) shall be interpreted to beinclusive (e.g., “x or y” means one or both x or y).

The term “and/or” shall also be interpreted to be inclusive (e.g., “xand/or y” means one or both x or y). In situations where “and/or” or“or” are used as a conjunction for a group of three or more items, thegroup should be interpreted to include one item alone, all of the itemstogether, or any combination or number of the items. Moreover, termsused in the specification and claims such as have, having, include, andincluding should be construed to be synonymous with the terms compriseand comprising.

Unless otherwise indicated, all numbers or expressions, such as thoseexpressing dimensions, physical characteristics, etc. used in thespecification (other than the claims) are understood as modified in allinstances by the term “approximately.” At the very least, and not as anattempt to limit the application of the doctrine of equivalents to theclaims, each numerical parameter recited in the specification or claimswhich is modified by the term “approximately” should at least beconstrued in light of the number of recited significant digits and byapplying ordinary rounding techniques.

All ranges disclosed herein are to be understood to encompass andprovide support for claims that recite any and all subranges or any andall individual values subsumed therein. For example, a stated range of 1to 10 should be considered to include and provide support for claimsthat recite any and all subranges or individual values that are betweenand/or inclusive of the minimum value of 1 and the maximum value of 10;that is, all subranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994,and so forth).

What is claimed is:
 1. A method comprising: reacting an organicfeedstock in a pressurized reactor, the organic feedstock being part ofa reaction mixture that includes sulfuric acid and nitric acid; andsupplying oxygen to the reaction mixture; wherein the reaction mixtureis at least 60° C.; and wherein the reaction mixture, excluding solids,includes no more than 7.5 wt % of the total of the sulfuric acid and thenitric acid.
 2. The method of claim 1 wherein the organic feedstockincludes sewage material.
 3. The method of claim 1 wherein the weightratio of solids in the organic feedstock to the total of the sulfuricacid and the nitric acid is at least 0.2.
 4. The method of claim 1wherein the weight ratio of solids in the organic feedstock to thenitric acid is at least 0.5.
 5. The method of claim 1 wherein the weightratio of solids in the organic feedstock to the sulfuric acid is atleast 0.3.
 6. The method of claim 1 wherein the pressure in the reactoris at least 1035 kPa.
 7. The method of claim 1 wherein the temperatureof the reaction mixture is at least 150° C.
 8. The method of claim 1wherein supplying oxygen to the reaction mixture includes supplyingoxygen gas to the reaction mixture.
 9. The method of claim 1 wherein thereaction mixture, excluding solids, includes no more than 5 wt % of thetotal of the sulfuric acid and the nitric acid.
 10. A method comprising:reacting an organic feedstock in a pressurized reactor, the organicfeedstock being part of a reaction mixture that includes sulfuric acidand nitric acid; and supplying oxygen to the reaction mixture; whereinthe reaction mixture is at least 60° C.; and wherein the reactionmixture, excluding solids, includes no more than 5 wt % of the sulfuricacid.
 11. The method of claim 10 wherein the organic feedstock includessewage material.
 12. The method of claim 10 wherein the weight ratio ofsolids in the organic feedstock to the total of the sulfuric acid andthe nitric acid is at least 0.2.
 13. The method of claim 10 wherein theweight ratio of solids in the organic feedstock to the nitric acid is atleast 0.5.
 14. The method of claim 10 wherein the weight ratio of solidsin the organic feedstock to the sulfuric acid is at least 0.3.
 15. Themethod of claim 10 wherein the pressure in the reactor is at least 1035kPa.
 16. The method of claim 10 wherein the temperature of the reactionmixture is at least 150° C.
 17. The method of claim 10 wherein supplyingoxygen to the reaction mixture includes supplying oxygen gas to thereaction mixture.
 18. The method of claim 10 wherein the reactionmixture, excluding solids, includes no more than 3 wt % of the sulfuricacid.
 19. A method comprising: reacting an organic feedstock in apressurized reactor, the organic feedstock being part of a reactionmixture that includes sulfuric acid and nitric acid; and supplyingoxygen to the reaction mixture; wherein the reaction mixture is at least60° C.; and wherein the reaction mixture, excluding solids, includes nomore than 1 wt % nitric acid.
 20. The method of claim 19 wherein theorganic feedstock includes sewage material.
 21. The method of claim 19wherein the weight ratio of solids in the organic feedstock to the totalof the sulfuric acid and the nitric acid is at least 0.2.
 22. The methodof claim 19 wherein the weight ratio of solids in the organic feedstockto the nitric acid is at least 0.5.
 23. The method of claim 19 whereinthe weight ratio of solids in the organic feedstock to the sulfuric acidis at least 0.3.
 24. The method of claim 19 wherein the pressure in thereactor is at least 1035 kPa.
 25. The method of claim 19 wherein thetemperature of the reaction mixture is at least 150° C.
 26. The methodof claim 19 wherein supplying oxygen to the reaction mixture includessupplying oxygen gas to the reaction mixture.